LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


Clas* 


WORKS  OF  FREDERICK  R.  HUTTON 

PUBLISHED    BY 

JOHN  WILEY  &  SONS 


The  Mechanical  Engineering:  of  Power  Plants. 

Third  Edition,  Rewritten.  8vo,  xli  +  825  pages,  and 
over  700  illustrations.  Cloth,  $5.00. 

Heat  and  Heat-engines. 

A  study  of  the  principles  which  underlie  t&e  mechan- 
ical engineering  of  a  power  plant.  8vo,  xxi  +  553  pages 
and  171  illustrations.  Cloth,  $5.00. 

The  Gas-engine. 

A  treatise  on  the  internal  combustion  engine  using 
gas,  gasoline,  kerosene,  alcohol,  or  other  hydrocarbon 
as  source  ot  energy.  Third  Edition,  Revised.  8vo, 
xx  4-  562  pages,  241  illustrations.  Cloth,  $5.00. 


THE    GAS-ENGINE 


A  TREATISE  ON  THE 


INTERNAL-COMBUSTION  ENGINE 

USING    GAS,    GASOLINE,    KEROSENE,    ALCOHOL, 

OR    OTHER    HYDROCARBON    AS 

SOURCE    OF   ENERGY. 


BY 


FREDERICK  REMSEN  BUTTON,  E.M.,   PH.D.,  Sc.D. 

Emeritus  Professor  of  Mechanical  Engineering  in  Columbia  University;   Past 
Secretary  and  President  of  the  American  Society  of  Mechanical  Engineers. 


THIRD   EDITION,    REVISED. 

FIRST    THOUSAND. 


NEW  YORK: 

JOHN  WILEY  &  SONS. 
LONDON:  CHAPMAN  &  HALL,  LIMITED. 

1908. 


6ENEAAL 


Copyright,  1903,  1907, 

BY 

FREDERICK  REMSEN  HUTTON. 


Hubert  Srummand  and  (Company 
Km  lurk 


PREFACE. 


WHEN  a  previous  treatise  by  the  author  was-  published  under 
the  title  of  "The  Mechanical  Engineering  of  Power  Plants," 
it  was  suggested  by  one  of  his  most  gifted  critics  that  the  title 
should  be  amended  because  the  book  did  not  cover  the  power- 
plant  practice  which  uses  gas-engines. 

The  point  was  well  taken,  but  the  omission  was  intentional. 
To  have  included  the  gas-engine  would  have  made  that  book 
inconveniently  bulky.  Furthermore,  the  treatment  of  the  gas- 
engine  must  be  essentially  different  from  that  given  to  the  steam- 
engine,  and  at  that  time  the  state  of  the  art,  both  practically 
and  scientifically,  did  not  admit  of  the  preparation  of  a  satis- 
factory and  exhaustive  discussion.  Since  that  time,  however, 
there  has  grown  up  a  largely  increased  appreciation  of  the  fuel 
value  of  what  were  called  the  waste  gases  from  the  blast-furnace, 
and  a  wider  extension  of  the  manufacture  of  fuel  gas  in  producers. 
The  gas-engine  has  been  extensively  applied  in  the  departments 
of  electric  lighting,  and  of  compression,  both  of  air  and  gas.  It 
is  since  that  time  also  that  there  has  appeared  the  exacting  de- 
mand for  motors  for  self-propelled  vehicles  and  for  small  launches, 
so  that  it  has  become  possible  to  undertake  that  for  which  the 
time  was  not  ripe  when  the  criticism  was  made.  There  was, 
at  that  time,  little  distinctively  American  practice  to  be  studied, 
but  the  principal  work  had  been  done  in  England,  Germany, 
and  Belgium.  The  introduction  by  Daimler  of  the  high-speed 
gas-engine  and  the  immediate  development  which  this  class 


179738 


iv  PREFACE. 

of  motor  received  in  France  for  motor- vehicle  use,  has  greatly 
stimulated  the  work  upon  this  class  of  machine  in  all  depart- 
ments. Furthermore,  the  development  of  the  carburetor  and 
the  recognition  of  the  significance  of  carburation  as  a  process  in 
the  handling  of  liquid  fuels,  enormously  widened  the  scope  and 
field  for  the  internal-combustion  motor.  In  fact,  in  the  opinion 
of  the  writer,  the  development  of  this  particular  detail  draws 
a  broad  line  of  distinction  between  the  former  and  present 
practice  which  marks  in  effect  an  epoch  of  the  development 
of  the  art. 

By  the  term  gas-engine  is,  therefore,  meant  the  internal- 
combustion  engine,  whether  using  gas  manufactured  without 
the  motor  and  delivered  to  it  as  combustible  gas,  or  making  its 
own  gas  by  carbureting  air  on  its  way  to  the  combustion-cham- 
ber. 

The  author  believes  that  a  very  important  field  is  open  for 
development  of  small  gas  producers  operating  on  coal  in  com- 
bination with  the  internal-combustion  engine  which  they  are  to 
serve.  It  will  be  apparent  that  by  either  the  liquid-fuel  system 
of  carburetting  air,  or  by  the  producer  system,  the  gas-engine 
reaps  all  the  advantages  which  follow  from  getting  rid  of  the 
boiler  and  its  plant  as  details  of  the  steam-generation  system 
whether  in  stationary,  marine,  or  motor-vehicle  practice. 

The  plan  and  scope  of  the  treatise  will  be  apparent  on  in- 
spection. The  starting-point  must,  obviously,  be  the  liberation 
of  the  energy  resident  in  fuels  in  the  form  of  heat  and  the  con- 
version of  that  heat  energy  into  mechanical  energy  with  the 
physical  laws  and  mathematical  principles  which  are  involved 
in  such  transformation.  The  cycle  of  operations  which  the  heat 
medium  undergoes  in  transforming  heat  energy  into  mechanical 
work  next  follows,  and  the  types  of  motor  in  which  these  trans- 
formations occur  with  gas,  gasoline,  kerosene,  and  alcohol  as. 
sources  of  the  combustible  hydrocarbon.  The  succeeding  chap- 
ters open  up  the  details  of  mechanically  effecting  the  mixture  of. 
fuel  and  air  for  the  internal  combustion  which  is  desired,  and 


PREFACE.  V 

the  methods  of  carburetting;  igniting,  and  governing.  The 
chapter  on  manipulation  is  intended  to  be  of  service  to  users  of 
engines  of  this  class,  although  as  a  rule  the  unsatisfactory  work- 
ing of  such  engines  is  the  consequence  of  defective  ignition,  car- 
buration  or  mixture,  already  discussed,  rather  than  the  con- 
sequence of  the  methods  of  manipulation.  This  part  concludes 
with  a  brief  presentation  in  compact  form  of  the  results  in  economy 
and  performance  as  determined  by  test. 

The  final  chapters  treat  of  the  mathematical  analysis  of  the 
laws  and  principles  whose  action  has  been  discussed  in  the  first 
part.  By  the  mathematical  form  of  this  analysis  it  becomes 
easy  to  use  the  results  of  the  analysis  in  a  quantitative  way  for 
a  comparison  of  cycles  or  with  a  view  to  studying  the  effects 
of  varying  these  cycles.  So  far  as  known,  this  part  of  the  work  is 
the  most  complete  treatment  which  has  yet  been  made,  and  it 
is  hoped  it  will  leave  little  to  be  desired  by  those  who  would 
find  a  study  of  this  sort  serviceable,  since  it  is  believed  to  be 
practically  exhaustive.  Especial  attention  should  be  called  to 
the  formula  for  theoretical  mean  effective  pressure.  The  de- 
velopment of  the  Otto  cycle,  by  reason  of  the  investment  of  capi- 
tal for  this  purpose,  has  thrown  into  comparative  obscurity  the 
important  possibilities  offered  by  the  other  type  of  internal- 
combustion  engines  in  which  the  heating  takes  place  at  constant 
pressure  rather  than  at  constant  volume.  A  chapter  is  given  to 
a  brief  treatment  of  this  particular  form  of  engine,  but  it  will 
be  apparent  that  this  is  the  opening  of  a  door  at  this  time  rather 
than  the  entering  upon  a  full  treatment.  If  the  continuous 
rotative  type  of  motor  is  to  be  developed  for  the  direct  utiliza- 
tion of  the  heat  energy  from  combustion,  it  is  likely  to  appear 
in  the  development  of  this  class  of  cycle.  But  at  this  time  the 
state  of  the  art  does  not  justify  the  giving  of  more  space  than  is 
allotted. 

The  book  concludes  with  some  general  statements  concern- 
ing explosive  mixtures,  an  historical  summary  and  a  brief  bibli- 
ography. 


VI  PREFACE. 

The  author,  in  conclusion,  must  express  his  obligation  and 
indebtedness  to  the  work  of  previous  writers  for  the  results  and 
data  which  they  have  made  as  contributions  to  the  arts  and 
sciences  whose  applications  have  developed  the  gas-engine. 
References  to  the  sources  from  which  these  data  are  taken  will 
be  found  through  the  text  or  in  the  titles.  He  would  express 
his  particular  obligation  to  Dr.  Charles  E.  Lucke,  who  is  asso- 
ciated with  him  in  the  work  of  education  and  research,  and  from 
*he  result  of  whose  work  with  his  permission  he  has  made  very 
liberal  drafts.  The  cyclic  analysis  in  Chapter  XVII  was  made 
by  Dr.  Lucke  while  a  graduate  student  under  the  author's  direc- 
tion, but  the  work  is  so  marked  by  originality  and  industry  in 
.the  prosecution  of  its  detail  that  Dr.  Lucke  should  receive  the 
full  credit  which  it  deserves  and  which  the  author  is  very  glad 
to  take  this  occasion  to  ascribe.  Dr.  Lucke  has  also  contributed 
much  of  signal  value  in  the  way  of  quantitative  experimental 
and  practical  data,  the  results  of  research  and  tests  in  the  labora- 
tory. The  author  would  express  his  thanks  also  to  Prof.  R.  H. 
Fernald  of  St.  Louis,  to  Mr.  T.  J.  Foster  of  Scranton,  and  to  Mr. 
E.  P.  Ingersoll,  and  others  to  whom  he  is  indebted  for  permission 
to  make  use  of  serviceable  illustrations  which  have  already  ap- 
peared elsewhere. 

No  attempt  has  been  made  to  enter  upon  the  field  of  the  design 
of  the  gas-engine  considered  as  a  machine.  This  field  of  engine 
design  has  been  -so  admirably  covered  by  others  with  respect 
to  the  steam-engine  and  the  same  principles  of  design  apply  so 
readily  to  the  gas-engine  with  the  necessary  modifications  intro- 
duced by  differences  in  principle,  that  this  subject  has  been  dis- 
regarded in  the  present  treatment.  The  exception  is  the  treat- 
ment of  the  cylinder  volume  as  a  derivative  from  the  transforma- 
tion of  heat  energy  into  mechanical  work  which  may,  perhaps> 
be  found  serviceable. 

F.  R.  HUTTON. 
COLUMBIA  UNIVERSITY, 

NEW  YORK, 
September,  1903. 


PREFACE   TO  THE  THIRD  EDITION. 


THE  practical  solution  of  a  problem  involving  the  applications 
of  natural  law  may  be  effectively  studied  from  two  view-points. 
The  one  is  the  functional  view-point,  involving  an  examination 
of  what  the  machine  does,  and  how.  The  second  is  the  quanti- 
tative examination  of  the  size  it  must  have,  to  do  a  certain  amount 
of  industrial  work  in  accordance  with  the  limits  set  by  natural 
laws.  Both  studies  are  necessary  for  successful  design,  but  the 
functional  idea  should  precede  the  quantitative  study. 

In  the  preparation  of  the  first  and  second  editions  of  this  text; 
the  first  idea  was  most  prominently  before  the  author's  mind, 
but  the  development  of  the  internal  combustion  motor,  and  the 
numbers  concerned  in  its  design  and  manufacture  have  made  it 
appear  desirable  to  amplify  certain  parts  of  the  treatment,  so 
as  to  cover  more  of  the  quantitative  requirement  of  the  engineer 
and  builder.  It  is  hoped  that  such  features  will  be  appreciated 
and  will  add  to  the  reference  value  of  the  book. 

Particular  attention  is  therefore  called  to  the  Reference  Table 
of  Gaseous  Fuels  in  connection  with  paragraph  29,  and  the 
availability  of  such  table  for  use  in  determining  Mean  Effective 
Pressure.  Too  great  emphasis  cannot  be  put  upon  the  import- 
ance of  using  the  exact  data  of  fact  in  the  making  of  guarantees 
of  efficiency  and  economy,  rather  than  the  unreliability  of  mere 
assertion,  and  this  table  is  intended  as  a  step  towards  making 
the  heating  value  of  the  fuel  the  ultimate  standard  of  these 
matters.  The  treatment  of  mean  effective  pressure,  of  effi- 
ciency, of  the  guarantee  and  considerable  expansions  of  the 
discussion  on  the  producer,  and  of  the  alcohols  as  fuels  are  all  new 
features  of  this  edition.  The  value  of  the  analysis  of  the  differ- 


viii  PREFACE  TO  THE   THIRD  EDITION. 

ent  cycles  is  also  increasing  as  more  attention  is  paid  to  these 
matters  by  both  engineers  and  the  public.  The  carburetor 
treatment  has  been  expanded  and  brought  more  up  to  date. 

In  the  previous  editions  the  treatment  of  the  design  of  engine 
parts  (paragraph  205)  has  been  intentionally  omitted.  It  is 
also  left  out  of  this,  not  only  because  of  the  inconvenient  bulk 
and  cost  which  it  would  entail  upon  the  book,  but  more  because 
of  the  appearance  of  the  book  by  a  colleague  and  co-worker  of 
the  author,  entitled  " Gas- Engine  Design,"  by  Prof.  Charles 
Edward  Lucke.  In  this  the  problems  of  inertia  effects,  balanc- 
ing, crank-effort  and  shaking  forces,  together  with  valve  propor- 
tions, fly-wheels,  cams,  springs,  and  other  parts  are  treated  so 
exhaustively,  and  in  so  scholarly  a  way,  that  to  include  these 
topics  herein  would  be  both  repetitious  and  superfluous.  The 
author  would  express  his  thanks  and  recognition  for  the  privilege 
of  incorporating  into  this  edition  certain  data  and  tabular  matter 
compiled  and  computed  by  Professor  Lucke  in  connection  with 
instruction  courses  in  which  both  books  have  been  used.  To 
Mr.  R.  E.  Mathot  of  Belgium  he  is  indebted  for  the  originals 
from  which  the  sections  of  foreign  gas-producers  have  been 
derived. 

It  is  the  hope  and  desire  of  the  author  that  the  teachers,  stud- 
ents, engineers,  manufacturers,  and  others  who  have  been  kind 
enough  to  commend  the  previous  editions,  will  find  this  new 
one  incorporating  suggested  alterations  even  more  useful  than 
its  predecessors. 

F.   R.   HUTTON. 

COLUMBIA  UNIVERSITY, 
September,  1907. 


TABLE  OF  CONTENTS. 


CHAPTER  I. 

INTRODUCTION. 
IRT.  PAGE 

1.  Sources  of  Motor  Energy 1 

2.  The  Limitations  of  Muscular  Force  and  the  Power  of  Gravity.-  3 

3.  Importance  of  Motor  Energy  Derivable  from  Heat 3 

4.  Analysis  of  a  Power-plant 4 

5.  Media  for  Use  in  Heat-engines 4 

6.  Sources  of  Heat  Energy : 6 

7.  Internal-combustion  Method  of  Heating  Air  as  a  Medium 7 

7a.  Analysis  of  the  Internal-combustion  Motor 9 

CHAPTER  II. 

LIBERATION  OF   HEAT  ENERGY.      COMBUSTION. 

8.  Introductory   12 

9.  Combustion,  Flame,  Smoke,  Incomplete  Cumbustion 12 

10.  Ignition.    Explosion.    Propagation  of  Flame.    Spontaneous  Com- 

bustion     15 

11.  Oxygen  and  Air  Required  for  Combustion  of  Carbon 21 

12.  Air   Required    for   Combustion   of    Hydrogen 23 

13.  Air  Required  for  Combustion  of  Compounds 24 

14.  Combustion  of   an   Analyzed  Fuel.     Combustion   Ratio 26 

15.  Calorific    Power   of   a   Fuel 30 

16.  Fuel   Calorimeters.     Mahler's    Bomb 33 

17.  The  Junker  Gas-calorimeter 35 

18.  The   Lucke   Gas-calorimeter 39 

19.  Calorific  Power  of  a  Compound 40 

20.  Computed  Increase  of  Temperature  Due  to  a  Combustion 41 

21.  Dissociation 43 

ix 


x  TABLE  OF  CONTENTS. 

ART.  ,  PAGE 

22.  Sources  of  Gaseous  Fuel  for  Gas-engines 43 

23.  Natural   Gas _ 44 

24.  Producer-gas 45 

25.  Water-gas    50 

25a.  Aspirating    Producers 55 

26.  Coal-gas  or  Illuminating-gas 64 

27.  Acetylene  Gas 64 

28.  Blast-furnace    Gas 65 

29.  Tables  of  Composition  and  Properties  of  Gases 71 

30.  Liquid  Fuel.     Petroleum 84 

31.  Pintsch  Oil-gas  86 

32.  Kerosene   86 

33.  Gasoline  88 

34.  Alcohol    90 

35.  Products  of  Combustion  of  a  Gas 97 

36.  The  Dilution  of  the  Mixture  of  Gas  and  Air 98 

37.  Gas   Analysis.     Elliot's   Gas-apparatus 101 

38.  Analysis  of  Products  of  Combustion.     Orsat's  Apparatus 102 


CHAPTER  III. 

MECHANICAL  ENERGY  FROM  EXPANSION  OF  GAS  AND  AIR. 

39.  Introductory.      Units    of    Mechanical    Energy.      Unit    of    Heat. 

Mechanical  Equivalent  of  Heat.    Horse-power 104 

40.  The  Piston  Motor.     Mean  Effective  Pressure 105 

40a.  Computed  Cylinder  Volume.     Diameter  and  Stroke 110 

41.  Graphical  Representation  of  the  Work  of  a  Piston  Motor.     The 

PV   Diagram 113 

42.  Gay-Lussac's  Law  for  Air 115 

43.  The  Law   of   Mariotte 115 

44.  The  Laws  of  Mariotte  and  Gay-Lussac  Combined 116 

45.  Absolute  Temperature.     Absolute  Zero 117 

46.  Total  or  Intrinsic  Energy.    Available  Energy 119 

47.  Efficiency.      Thermal    Efficiency 121 

47a.  Mechanical    Efficiency 124 

47b.  Combined  Mechanical  and  Thermal  Efficiency. — The  Guarantee.-  126 

48.  Expansive  Working  of  Media  Compared  with  Non-expansive 128 

49.  Isothermal  Expansion 130 

50.  Adiabatic   Expansion 131 

51.  Aiabatic  Work  in  Terms  of  Pressures ___  132 

52.  Temperature  Change  in  Adiabatic  Expansion 133 


TABLE  OF  CONTENTS.  xi 


53.  Other  Thermal  Lines.     Isometric.     Isopiestic.     Isobars 134 

54.  Specific  Heat  at  Constant  Pressure  and  at  Constant  Volume .  136 

55.  Effective    Specific    Heat 1 141 

56.  Value  of  the  Exponent  y  in  the  Equation  for  Expansion ,  147 

57.  The   Continuous   Rotative   Motor   Using   Pressure,    Impulse,   or 

Reaction    151 


CHAPTER  IV. 

THE    HEAT    ENGINE    CYCLE. 

58.  Introductory    152 

59.  The  Cycle  of  the  Steam-engine 153 

60.  The    Carnot    Cycle 154 

61.  The  Cycle  of  the  Internal-combustion  Engine 157 

62.  The  Otto  Cycle  with  Heating  at  Constant  Volume 158 

63.  The  Brayton  Cycle  with  Heating  at  Constant  Pressure 162 

64.  The  Diesel  Cycle  with  Heating  at  Constant  Temperature 163 

65.  Advantages  of  the  Internal-combustion  Principle 163 

66.  Disadvantages  of  the  Internal-combustion  Principle 167 

67.  Variations    in    Cycle 170 


CHAPTER  V. 

GAS-ENGINES  BURNING  GAS. 

68.  Introductory 171 

69.  The    Otto    Engine 171 

70.  The   Nash    Engine I 175 

71.  The    Korting    Engine 177 

72.  The   Westinghouse  Engine 177 

73.  The    Two-cycle    Engine 180 

74.  Comparison  of  Types 184 

75.  Other   Forms   of   Gas-engine 185* 

76.  The   Compound   Gas-engine _  187 


CHAPTER  VI. 

GAS  ENGINES   USING  KEROSENE  OIL. 

77.  Introductory  188 

78.  The    Priestman    Engine 188 

79.  The   Hornsby-Akroyd   Engine _ 189 

80.  The  Secor  Kerosene  Engine ,  _  190 


TABLE  OF  CONTENTS. 


81.  The  Mietz  and  Weiss  Engine :__  191 

82.  The  Diesel  Engine.     The  Hirsch  Engine 193 

83.  The  Verplanck-Lucfce  Kerosene   Engine 195 

84.  Comparison    of    Types 197 

CHAPTER  VII. 

GAS    ENGINES    USING    GASOLINE        AUTOMOBILE    ENGINES. 

85.  Introductory    198 

86.  The  Air-cooled  Bicycle  Motor 199 

87.  The  Air-cooled  Automobile  Motor 201 

88.  The  Water-cooled  Automobile  Motor 201 

89.  Variations  in  the  Automobile  Motor 203 

90.  The   Launch   Engine 204 

91.  Converted   Gas-engines 205 

CHAPTER  VIII. 

ALCOHOL-ENGINES. 

92.  Introductory  207 

93.  The  Alcohol-automobile  Motor.     The  Gobron-Brillie 208 

94.  The  Alcohol-launch  Engine 209 

CHAPTER  IX. 

PROPORTIONING   OF    MIXTURES. 

95.  Introductory  211 

96.  Automatic  Mixing  by  Suction 212 

97.  Proportioning  by  Adjustable  Valves 213 

98.  Proportioning  by  Mechanically  Operated  Valves 214 

99.  Proportioning  by  Volumes  of  Pump  Cylinders 215 

100.  Proportioning  by  Control  of  the  Carbureter 216 

101.  Effect   of    Scavenging 216 

102.  Effect  ofVariation  in  the  Mixture 217 

103.  Effect  of  Speed  Variations  in  Varying  the  Mixtures 218 

CHAPTER  X. 

CARBURATION    AND    CARBURETERS. 

105.  Introductory  221 

106.  The  Surface  Carbureter,  De  Dion  Motor- cycle  Type 22,3 

107.  Wick  or  Flannel  Carburetors 225 


TABLE  OF  CONTENTS.  xiii 

ART.  PAGE 

108.  Carburation  from  a  Gauze  Surface.     Olds  Type 228 

109.  Carburation  by  Mechanical  Ebullition.     Daimler  Type 229 

110.  Spray  Carburetors,  Float-feed  Type.     Maybach's 229 

111.  Float   Carburetors    with    Constant-level    and    Distributing   Cone. 

Phoenix,  Daimler,  and  Longuemare 230 

112.  Float  Carburetor  with  Constant  Level,  with  Baffle-plates.    Axiom  232 

113.  Carburetors  without  Floats 232 

114.  Carburetors  for  Motor  Vehicles.    Automatic  Carburetors 236 

115.  Alcohol  Carburetors.     Martha,  Japy,  Richard,  Brouhot,  Marien- 

felde  245 

116.  Kerosene  Carburetors 247 

117.  Some  Principles  of  Design  of  Carburetors 249 

CHAPTER  XI. 

IGNITION. 

120.  Introductory 250 

121.  Ignition  by  Auxiliary  Flame 250 

122.  Ignition  by  Internal  Flame 251 

123.  Ignition  by  Heated  Metal  from  External  Jet 251 

124.  Ignition    by    Catalysis 252 

125.  Ignition  by  Incandescent  Wire  or  Cage  Electrically  Heated 252 

126.  Ignition  by  Hot  Tube 252 

127.  Ignition  by  High  Temperature  of   Compression 255 

128.  Ignition  by  Electrodes   and  Electric   Sparks.     The  Jump-spark 

System 256 

129.  Ignition  by  Electric  Arc.     Hammer-break  System 260 

130.  Dynamo  or  Magneto-electrical  Ignition.     General 262 

CHAPTER  XII. 

GOVERNING. 

135.  Introductory  264 

136.  Governing  by  Missing  a  Charge.    The  Hit-or-miss  Governor 266 

137.  Governing  by  Impoverishing  the  Charge 267 

138.  Governing  by  Throttling  the   Normal  Charge 267 

139.  Governing  by  Throttling  the  Exhaust 269 

140.  Governing  by  Retarding  the   Ignition 269 

141.  Governing  by  Advancing   the    Spark,    Pre-igniting   the   Mixture  272 

142.  Governing  by  Cutting    off    Admission 273 

143.  Governing  in  the    Two-cycle    System „ 274 

144.  Limitations  of  the  Gas-engine  by  the  Problem  of  Governing 274 


XIV  TABLE  OF  CONTENTS. 

CHAPTER  XIII. 

THE    COOLING    OF    THE    CYLINDER. 
ART.  PAGE 

145.  Introductory    279 

146.  Cooling  by  Injection  into  the  Air,  into  the  Expanded  Gases,  into 

the  Products  of  Combustion 279 

147.  Cooling  of  Metal  by  Water-jacket,  the  Steam  to  be  Utilized  or 

Wasted   - 280 

148.  Water-cooling   of    the    Piston 282 

149.  Cooling  by  Air-jacket  — 282 

150.  The  Circulation  of  the  Cooling  Water  and  the  Amount  Required 

for   Cooling 283 

CHAPTER  XIV. 

THE  COMBUSTION-CHAMBER  AND  THE  EXHAUST. 

151.  Introductory    285 

152.  Volume  of   the   Combustion-chamber 286 

153.  Form   of   the   Combustion-chamber 292 

154.  The  Disposal  of  the  Exhaust-gases 292 

155.  Back-pressure    of    Exhaust-gases 293 

156.  Muffling  of  the  Exhaust 294 

CHAPTER  XV. 

MANIPULATION   OF   GAS   ENGINES. 

160.  Introductory  297 

161.  Effects  of  Quality  or  Richness  of  the  Gas 297 

162.  The   Starting  of  the  Engine 298 

163.  The  Stopping  of  the  Engine 301 

164.  Restarting  after  a   Stop  302 

165.  The  Lubrication  of  the  Engine 307 

166.  Improper  Working  of  the  Engine;  the  Engine  Refuses  to  Start 

or  Work 308 

167.  Usual  Causes  of  Failure  to  Operate 313 

168.  Concluding    Summary 315 

CHAPTER  XVI. 

THE  PERFORMANCE  OF  GAS-ENGINES  BY  TEST. 

170.  Introductory    317 

171.  The  Indicator  for  Gas-engine  Testing 320 


TABLE  OF  CONTENTS.  xv 

FIG.  PAGE 

172.  The  Apparatus  for  a  Test 321 

173.  Fernald's  and  Lucke's  Apparatus  to  Observe  Exhaust  Temper- 

atures     322 

174.  The  Observation  in  a  Test  327 

175.  The  Precautions  against  Error  in  a  Test 340 

176.  The  Conclusions  from  a  Test 341 

177.  Records  of  Perfomance  and  Economy  of  the  Gas-engine 341 

178.  Sources  of  Loss  in  Actual  Engines  as  Compared  with  the  Ideal  344 

CHAPTER  XVII. 

THEORETICAL    ANALYSIS    OF    THE    GAS-ENGINE. 

180.  Introductory    , 346 

181.  The  Temperature  Entropy  Diagram 346 

182.  Changes  in  Value  of  0  when  Heat  is  Added  to  Air 349 

183.  Analysis  of  Possible  Cycles  in  the  Internal-combustion  Engine 

Non-compression  Cycles 351 

184.  Compression  Cycle  with  Isometric  Heating 375 

185.  Compression  Cycle  with  Isopiestic  Heating 389 

186.  Compression  Cycle  with  Isothermal  Heating 401 

187.  Compression  Cycle  with  Heating  Process  Arbitrary 416 

188.  Cycles  with  Atmospheric  Heating 417 

189.  Comparison  of  Cycles  with  Respect  to  Temperatures  before  Ex- 

pansion     429 

190.  Comparison  of  Cycles  with  Respect  to  Temperatures  after  Ex- 

pansion     432 

191.  Deduction  from  Comparisons  of  Cycles  with  Respect  to  Tem- 

perature in  the  Various  Cycles 434 

192.  Comparison  of  Cycles  with  Respect  to  Pressures  after  Addition 

of  Heat  before  Expansion 436 

193.  Comparison  of  Cycles  with  Respect  to  Pressures  after  Expansion  438 

194.  Comparison  of  Mean  Effective  Pressures  in  the  Various  Cycles  440 

195.  Comparison  of  Cycles  with  Respect  to  Volumes  after  Heating 

and  before  Expansion 446 

196.  Comparison  of  Cycles  with  Respect  to  Volumes  after  Expansion  448 

197.  Deductions  from  Comparisons  of  Cycles  with  Respect  to  Volumes  452 

198.  Comparison  of  Cycles  with  Respect  to  Heat  Discharged  or  Ab- 

stracted.   Work  Done.     Efficiencies 455 

199.  General  Conclusions  from  the  Analysis  of  Cycles 463 

200.  Formula  for  Theoretical  Mean  Effective  Pressure.     Otto  Cycle  469 

201.  Factors  Reducing  Computed  Mean  Effective  Pressure.    Diagram 

Factor 476 

202.  Design  of   Cylinder  Volumes „ 480 


xvi  TABLE  OF  CONTENTS. 

ART.  PAGE 

203.  Volume  of  the  Clearance 481 

204.  Velocity  through  Valves,  Ports,  and  Passages 483 

205.  Mechanical  Design  of  Gas-engines  Regarded  as  Machines 483 

CHAPTER  XVIII. 

INTERNAL-COMBUSTION   ENGINES    WITH    HEATING  AT   CONSTANT   PRESSURE. 

210.  Introductory    485 

211.  Lucke    Apparatus    for    Continuous    Combustion    of    Explosive 

Mixtures    486 

212.  Engines  which  have  Operated  with  Constant-pressure   Heating  494 

213.  The  Brayton  Engine 497 

214.  Apparatus    for   Observing   Increase   in   Volume  with   Constant- 

pressure    Heating 499 

215.  The  Future  of  the  Engine  which  Uses  Constant-oressure  Heat- 

ing of  the  Working  Medium.    The  Gas-turbine 500 

CHAPTER  XIX. 

EXPERIMENTS   ON   EXPLOSIVE   MIXTURES. 

220.  Introductory    ___  502 

221.  Clerk's  Explosion  Experiments 504 

222.  Lucke's   Explosion   Experiments 507 

223.  The    Massachusetts    Institute    of    Technology    Experiments    on 

Explosive    Mixtures -. 514 

224.  Grover's  Experiments  with  Acetylene 518 

225.  Grover's  Experiments  on  Effect  of  Neutrals  in  Explosive  Mix- 

tures     522 

226.  Temperature  of  Ignition  or  Inflammation 523 

227.  The  Rate  of  Propagation  of  Flame 525 

228.  The  Propagation  of  an  Explosive  Wave 526 

229.  Concluding    Comment 528 

CHAPTER  XX. 

COSTS  OF  OPERATION. 

230.  Introductory    529 

231.  The  Elements  of  Cost 531 

232.  The  Fuel  Cost  and  Guarantee , 539 

CHAPTER  XXL 

CONCLUSION. 

240.     Historical    Summary 542 

250.     Bibliography  545 

260.    Appendix.    Table  of  Hyperbolic  Logarithms 549 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Mahler   Bomb   Calorimeter . 34 

2.  Junker    Gas-calorimeter — Elevation 35 

3.  Junker    Gas-calorimeter — Section 37 

4.  Lucke  Gas-calorimeter 39 

5.  Siemens    Producer   48 

6.  Taylor    Producer 49 

7.  Taylor    Producer— Detail 49 

8.  Dowson    Producer 51 

9.  Lencauchez    Producer 52 

10.  General  Elevation  of  Producer-plant 54 

11.  Blast-furnace  Gas-engine 70 

12.  Diagram  of  Pressures  Due  to  Combustion 100 

13.  Elliott   Gas-analysis   Apparatus 101 

14.  Orsat  Gas-analysis  Apparatus ' 103 

15.  Rectangular  PV  Diagram 113 

16.  Typical  PV   Diagram 114 

17.  Typical  PV  Diagram 129 

18.  Isothermal  Expansion  Curve 130 

19.  Adiabatic   Expansion  Curve 131 

20.  Isometric  Line 135 

21.  Isopiestic  Line 135 

22.  Typical  Gas-engine  Card  for  n 148 

23.  Typical  Gas-engine  Card  for  n 149 

24.  Typical  Gas-engine  Card  for  n 149 

25.  Carnot  Cycle  Diagram 155 

26.  Diagram  of  Otto  Cycle 159 

27.  Diagram  of  Otto  Cycle 160 

28.  Otto  Cycle  Connected  to  Motor-piston 160 

29.  Otto  Cycle  Connected  to  Motor-piston 161 

30.  Diagram  of  Crank-effort 162 

31.  Plan  of  Otto  Engine 172 

32.  Section  of  Clerk  Engine 175 

xvii 


xvill  LIST  OF  ILLUSTRATIONS 

FIG.  PAGE 

33.  Nash  Engine — Section 176 

34.  Korting   Engine faces  177 

35.  Westinghouse  Engine — Section faces  178 

36.  Westinghouse  Governor  Valve 179 

37.  Westinghouse  Double-acting  Horizontal 180 

38.  Lozier  Two-cycle  Engine 181 

39.  Lozier  Two-cycle  Engine 181 

40.  Lozier  Two-cycle  Engine 182 

41.  Secor  Kerosene  Engine faces  190 

42.  Diesel    Engine — Section 191 

43.  Diesel  Engine— Section 192 

44.  Diesel  Engine — Three-cylinder  Design 193 

45.  Diesel  Engine— Card 194 

46.  Hirsch  Engine — Elevation 195 

47.  Hirsch  Engine— Card 196 

48.  Gobron-Brillie    Alcohol    Motor 209 

49.  Olds   Mechanically   Operated   Valves 215 

50.  Marsh  Motor-bicycle 200 

51.  Daimler    Automobile    Motor 202 

52.  Daimler    Automobile    Motor 203 

53.  De  Dion   Surface   Carburetor 223 

54.  De  Dion   Surface   Carburetor— Detail 224 

55.  Felt  or  Wick  Carburetor 225 

56.  Felt   or   Wick   Carburetor— Brayton 226 

57.  Wick   or   Flannel    Carburetor 227 

58.  Wick   or   Flannel    Carburetor 227 

59.  Gauze    Surface    Carburetor 228 

60.  Gauze    Surface    Carburetor— Attached 228 

61.  Carburetor    Using   Mechanical    Ebullition — Daimler 229 

62.  Carburetor    with    Float— Maybach 230 

63.  Carburetor  with  Float— Daimler  (Phoenix) 231 

64.  Carburetor   with   Float — Longuemare 231 

65.  Carburetor    with    Float — Axiom 233 

66.  Carburetor   without   Float — James    Lunkenheimer 233 

67.  Carburetor  without  Float — Huzelstein 234 

68.  Carburetor  with  or  without  Float 236 

69.  Carburetor   for   Alcohol   and   Gasoline — Marienfelde 245 

70.  Carburetor    for    Alcohol— Martha 246 

71.  Carburetor   for   Alcohol— Brouhot 247 

72.  Carburetor    for    Alcohol— Richard 248 

73.  Carburetor    for    Alcohol— Japy : 248 

74.  Aspirating   Producer,    Belgian 56 

75.  Loomis-Pettibone    Producer 58 


LIST  OF  ILLUSTRATIONS.  xix 


76.  Hot-tube    Igniter 253 

77.  General  Electrical  Ignition  System 256 

78.  Sparking-plug    257 

79.  Electric  Igniter,  Primary,  Jump-spark 258 

80.  Electric   Igniter,   Mechanical   Vibrator 259 

81.  Electrical  Ignition — Advancing  Spark 260 

82.  Electrical    Ignition — Hammer-break 261 

83.  Governor   Detail,   on  Throttle-valve 265 

84.  Throttle-valve  Detail,  Winton 268 

85.  Ignition  Line  of  Gas-engine  Diagram 270 

86.  Ignition   Line   at   Dead-point 271 

87.  Ignition  Line  Retarded  Y^" 2?1 

88.  Ignition    Line    Advanced 272 

89.  Gas-engine   Indicator  Diagram — Sargent 273 

90.  Muffler    Designs . 273 

91.  Engine  Scheme,  Showing  Muffler  296 

92.  Clark-Lanchester  Starting  Scheme 306 

93.  Lever-brake  Dynamometer 318 

94.  Rope-brake   Dynamometer 319 

95.  Gas-engine  Indicator 320 

96.  Indicator    Rigging 321 

97.  Fernald  and  Lucke's  Exhaust  Temperature  Apparatus 323 

100.  00  Diagram  348 

101.  00  Diagram 348 

102.  00  Diagram  350 

111-151.  PV  Diagram,  Cycle  I  to  IX ,353-423 

112-152    00  Diagram,  Cycle  I  to  IX 353-423 

153—161.  Temperatures  in  Various  Cycles,  Quantitative 426-428 

162-166.  Temperatures  in  Various  Cycles,  Quantitative 430-432 

167.     Diagram  of  Mean  Effective  Temperatures 436 

168-171.  Diagram  of  Pressures 436-439 

172-180.  Diagram  of  Mean  Effective  Pressures 440-444 

181-190.  Diagram  of  Volumes 447-454 

192-198.  Diagram  of  Work  Done,  Various  Cycles 456-459 

199-205.  Diagram  of  Efficiencies,  Various  Cycles 459-460 

206.    Diagram   for  M.E.P 470-472 

210.  Lucke  Device  for  Burning  Explosive  Mixtures 489 

211.  Lucke  Device  for  Burning  Explosive  Mixtures 490 

212.  Lucke  Device  for  Burning  Explosive  Mixtures 491 

213.  Lucke  Device  for  Burning  Explosive  Mixtures 492 

214.  Wilcox  Engine,  with  Constant-pressure  Heating 494 

215.  Gibbs  Engine,  with  Constant-pressure  Heating 495 

216.  Schmid  &  Beckfield  Nozzle-pressure  Heating 495 


xx  LIST  OF  ILLUSTRATIONS. 


217.  Reeve  Design  for  Pressure  Heating . 496 

218.  Brayton  Engine,  Constant-pressure  Heating 497 

219.  Brayton  Carburetor 498 

220.  Steam  and  Products  of  Combustion  Engine 498 

221.  Lucke  Apparatus  for  Observing  Increase  in  Volume 499 

222.  Curve  of  Temperature  of  Combustion  of  Gas  and  Air 503 

225.  Clerk's  Explosion  Apparatus  504 

226.  Clerk's  Explosion  Curves 505 

227.  Lucke  Apparatus  for  Explosion  Pressures 507 

228.  Calorific  Power  of  Gas-air  Mixtures 510 

229-231.  Explosion  Pressures  with  Varying  Composition  of  Mixtures.  513 
232-234.  Explosion  Pressures  with  Varying  Composition  of  Mixtures.  513 

235.  M.I.T.   Explosion  Experiments 516 

236.  M.I.T.   Explosion   Experiments 518 

237-239.  Grover's  Explosion  Experiments  with  Acetylene 519-520 

240-242.  Grover's  Explosion  Experiments  with  Acetylene 520-521 

243.  Grover's  Experiments  on  Effect  of  Neutrals 523 

244.  Analysis  of  Internal  Combustion  Motor 11 

245.  English  Mond  Producer 50 

246.  Tangye  Suction  Producer 59 

248-250.  Foreign  Gas  Producers 61-63 

251.  Compression-curve  for  Air 238 

252.  Three-port  Two-cycle  Engine 183 

253.  Piston  of  Two-cycle  Engines 182 

254.  Carburetor— Schebler  240 

255.  Carburetor— Holly   .241 

256.  Carburetor — Bowers 241 

258.  Carburetor  Motor  Vehicle 242 

259.  Carburetor  Motor  Vehicle  _.  .  243 


THE  GAS-ENGINE. 


CHAPTER  I. 

INTRODUCTORY. 

1.  Sources  of  Motor  Energy. — There   are  three  important 
sources  of  power  or  energy  for  industrial  uses.    The  first  is  known 
as   muscular  power  and  is  that  which  resides  in  the   contractile 
tissue  of  the  muscles  in  man  and  animals.     The  second  is  the 
force  by  which  the  earth  attracts  all  masses  towards   its  centre, 
which  produces  weight  and  the  acceleration  due  to  gravity.    The 
third  is  a  group  of  forces  which  become  manifest  or  are  released 
upon  chemical  reactions  such  as  occur  in  combustion  or  oxida- 
tion; the  two   most   important   manifestations    of  these  are   the 
forces  of  electricity  and  of  heat. 

2.  The  Limitations  of  Muscular  Force   and  the  Power  of 
Gravity. — There  are  certain  fixed  limits  set  to  the  amount  of 
energy  which  can  be  made  available  from  any  single  unit,  either 
of  men  or  of  animals. 

While  this  limit  will  vary  with  the  muscular  endowment  of 
the  individual,  and  further  with  his  temperament,  his  training, 
his  health,  his  size,  his  race,  and  his  species,  it  will  be  obvious 
that  large  powers  can  only  be  obtained  by  aggregating  many 
such  units.  This  is  inconvenient  and  costly,  but  even  more  than 
this,  a  definite  limit  is  set  by  the  endurance  of  the  animal  unit, 
which  must  have  periods  of  rest  and  recuperation.  The  speed 
of  such  units  is  also  limited  by  the  ability  of  the  animal  motor 


2  THE   G4S-ENGINE. 

to  maintain  his  maximum  effort  for  any  length  of  time.  There 
is,  finally,  no  considerable  reserve  of  energy  in  storage  to  be 
drawn  upon  in  case  the  resistance  should  be  temporarily  in- 
creased. 

The  power  due  to  gravity  becomes  available  for  motor  uses  when 
a  weight  or  mass  is  lifted  to  a  higher  level  and  is  permitted  to 
descend  to  a  lower  one.  Solid  weights  are  only  serviceable 
when  lifted  by  some  other  mechanical  force;  water  and  air  are 
the  only  weights  which  are  otherwise  lifted,  independent  of  man, 
to  a  distance  farther  from  the  centre  of  the  earth.  Water  is 
lifted  by  the  sun  in  vapor,  to  be  deposited  on  the  high  levels  of 
the  land,  whence  it  seeks  to  descend  again  to  the  tide-water  levels ; 
the  winds  which  drive  wind-motors  are  caused  by  the  descent 
of  the  cold  air  from  upper  levels  of  the  atmosphere  to  the  lower 
levels  by  reason  of  its  greater  weight  per  unit  of  bulk  which  tends 
to  displace  the  air  which  has  been  warmed  by  the  earth.  It  is 
obvious,  therefore,  that  gravity,  as  a  motive  power,  is  dependent 
upon  the  availability  of  higher  levels  of  land  at  which  a  sufficient 
mass  of  water  can  be  accumulated;  and  an  adequate  reservoir 
in  any  particular  region  or  an  adequate  flow  from  a  source, 
together  with  an  available  difference  of  level,  are  necessary  con- 
ditions for  the  use  of  water-motors.  With  respect  to  windmills, 
it  must  as  yet  be  said  that  while  there  is  an  abundance  of  energy 
present  in  the  atmospheric  ocean,  at  the  bottom  of  which  all  the 
industries  of  the  earth  are  carried  on,  yet  the  reliability,  capacity, 
and  controllability  which  must  attach  to  a  satisfactory  industrial 
motor  are  not  found  in  most  places.  The  exceptions  are  where 
windmills  may  be  used  for  pumping  or  to  store  some  other  form 
of  energy  in  accumulators  or  otherwise,  to  be  given  out  as  required. 

This  same  series  of  difficulties  has  beset  the  successful  appli- 
cation of  the  energy  stored  by  the  winds  and  other  disturbances 
in  the  waves  of  the  ocean.  Tide-motors  depend  upon  the  lifting 
of  the  ocean  level  by  stellar  or  planetary  attractions  and  are 
reliable  and  controllable  within  the  limits  of  their  capacity. 
They  are  only  made  of  large  capacity  at  great  cost.  The  types 


INTRODUCTORY.  3 

of  motors  so  far  proposed  to  utilize  either  the  impact  of  ocean 
waves  or  the  lifting  force  of  the  continuous  wave  near  the  coast: 
have  not  proved  reliable  nor  permanent  enough  for  engineers  to^ 
venture  to  adopt  or  install  them  as  a  source  of  continuous  energy. 

It  will  be  apparent  that  since  it  is  the  energy  of  the  sun  which 
lifts  the  water  to  higher  levels  of  land  and  which  disturbs  the 
equilibrium  of  the  strata  of  air,  there  is  a  figurative  sense  in 
which  both  water-motors  and  windmills  can  be  called  heat- 
motors  in  the  last  reduction. 

3.  Importance  of  Motor  Energy  Derivable  from  Heat. — 
It  will  be  at  once  apparent  that  while  the  energy  resident  in 
falling  water  is  most  serviceable  and  is  destined,  doubtless,  to 
become  more  so  as  the  means  of  transmitting  energy  are  im- 
proved, yet  there  are  many  causes  which  make  the  form  of  motor 
utilizing  the  energy  liberated  in  the  form  of  heat  to  be  by  far 
the  most  considerable.  The  energy  due  to  falling  water  is,  with  a 
few  notable  exceptions,  limited  in  amount  both  by  the  weight 
available  and  by  the  height  of  the  fall.  The'  weight  available 
becomes  uncertain  when  by  reason  of  diminishing  rainfall  the 
amount  of  water  received  upon  any  watershed  becomes  dimin- 
ished. In  the  case  of  the  energy  derived  from  the  combustion  of 
a  fuel  furnishing  heat,  there  is  stored  an  amount  of  available 
energy  limited  only  by  the  supply  of  such  combustible  fuel. 
The  energy,  moreover,  is  in  compact  bulk,  and  in  the  form  of 
compressed  gas  or  in  the  liquid  fuels  it  is  of  comparatively 
light  weight  with  respect  to  the  amount  of  energy  which  it  can 
furnish.  For  these  reasons  the  importance  of  the  study  of  heat- 
motors  is  very  great  under  the  present  conditions  of  industry, 
and  the  exceeding  convenience  which  attaches  to  the  gas-engine 
as  a  means  of  utilizing  the  energy  of  combustible  fuel  has  been 
continually  receiving  increased  consideration. 

While  it  is  not  difficult  to  believe  that  the  near  future  may 
reveal  methods  for  generating  or  liberating  energy  directly  from 
a  fuel  in  the  form  of  electromotive  force  and  current,  and  this 
is  now  done  where  the  chemical  reactions  in  the  various  electrical 


4  THE   GAS-ENGINE. 

batteries  release  such  force  and  current,  yet,  at  this  writing,  the 
importance  and  extent  of  the  applications  of  such  methods  place 
them  in  the  field  of  the  physicist  and  the  experimenter  rather 
than  in  that  of  the  engineer  concerned  with  industrial  problems. 

4.  Analysis  of  a  Power-plant. — The  industrial  result   in  a 
power-plant  is  the  production  of  something  which  shall  have  a 
commercial   or   salable   value.     This   may   be   a   manufactured 
article  or  it  may  be  the  transportation  of  persons  or  of  goods  for 
industrial  purposes,  or  for  pleasure,  for  which  the  community 
shall  be  willing  to  pay.     It  will  be  apparent,  therefore,  that  the 
last  link  in  a  power-generating  chain  will  be  as  extensive  as  the 
entire  field  of  industry.     The  transmission  to  the  machines  or 
appliances  which  utilize  the  energy  is  also  a  field  of  wide  extent 
which  will  be  greatly  conditioned  by  the  purpose  for  which  the 
power  is  to  be  used.     For  these  reasons  it  also  may  be  excluded 
from  the  present  field  of  consideration  and  attention  paid  only 
to  the  problems  connected  with  the  liberation  of  the  energy  or 
the  generation  of  the  power  in  a  device  or  appliance  which  is 
fitted  to  receive  the  energy  liberated  from  the  combustible  fuel 
and  manifested  in  the  form  of  a  force  exerted  through  a  space. 
The   problem   of   the   heat-engine,    therefore,    has   two    distinct 
divisions.     The  first  is  the  liberation  of  the  heat  energy  and  its 
transfer  to  a  medium  capable  of  exerting  mechanical  energy. 
The  second  division  is  the  motor  or  engine  to  receive  this  mechan- 
ical energy  and  to  put  it  into  usable  form.     The  development 
in  the  subsequent  chapters  will  follow  the  lines  of  these  two 
divisions. 

5.  Media  for  Use    in  Heat-engines. — In  the   selection  of  a 
medium  to  receive  the  energy  liberated  from  a  source  of  heat  it 
will  be  apparent  that  the  considerations  are  both  scientific  or 
physical,    and    commercial    or   practical.     The    first    and   most 
obvious  phenomenon  which  occurs  upon  the  increasing  of  the 
heat  energy  in  a  body  is  an  increase  in  its  bulk  or  volume.     The 
gases  undergo  the  greatest  change  in  bulk  or  volume  for  a  given 
increase  in  their  amount  of  heat  energy,  and  would  naturally 


INTRODUCTORY.  5 

be  those  which  would  be  first  chosen  as  media.  While  solids 
and  liquids  also  undergo  a  similar  dilatation,  it  is  less  in  extent, 
although  capable,  within  the  range  of  such  dilatation,  of  exerting 
a  force  of  much  greater  intensity.  By  the  use  of  gases  which 
change  their  shape  or  figure  very  easily  within  a  containing 
envelope,  and  which  have  small  density  or  weight  per  cubic 
foot,  the  flow  of  such  media  through  pipes  and  passages  is  more 
rapid  and  is  less  affected  by  friction  or  other  resistance.  Among 
the  media,  they  will  be  found  to  differ  among  each  other  accord- 
ing to  the  ease  with  which  different  materials  will  pass  from  the 
gaseous  state  into  a  liquid  form.  Steam,  which  is  the  result  of 
evaporating  water  into  a  gas,  is  the  most  convenient  example 
of  such  media  as  change  their  state  easily  within  the  limits  which 
are  within  convenient  reach.  Other  such  media  are: 

Ammonia  (NH3); 

Acetone  (C3H6O); 

Alcohol  (C2H6O); 

Bisulphide  of  carbon  (CS2); 

Chloride  of  carbon  (CC14)  * 

Chloroform  (CHC13) : 

Ether  (C4H100); 

Naphtha  and  gasoline  (C6H14  to  C8H18). 

These  have  the  advantage  of  making  the  change  from  liquid 
to  vapor  at  temperatures  lower  than  is  necessary  for  steam,  but 
are  open  to  the  serious  objections  on  the  practical  side  that 
they  are  costly  and  require  to  be  operated  in  such  a  form  of  engine 
as  shall  permit  that  after  the  use  in  the  motor  proper  the  escaping 
vapor  shall  be  condensed  back  to  liquid  so  as  to  be  used  over 
again  continuously.  They  are  also  open  to  objections  either 
by  reason  of  an  offensive  or  pungent  odor,  or  because  they  are 
inflammable  or  explosive,  or  produce  some  physiological  effect 
on  the  human  organism.  Some  are  poisonous  and  irrespirable. 
These  are  competitors  with  steam  as  a  medium  rather  than  with 
air. 


6  THE  GAS-ENGINE. 

Air,  on  the  other  hand,  as  a  medium  is  cheap,  safe,  odorless, 
innoxious,  non-inflammable,  and  very  accessible.  It  has  the 
advantage,  furthermore,  of  being  able  to  be  used  with  a  direct 
contact  with  the  flame  which  is  a  manifestation  of  the  liberation 
of  the  heat  energy,  which  the  others  are  not  capable  of  doing. 
The  importance  of  the  air  as  a  medium  is,  therefore,  sufficient 
to  make  it  possible  to  confine  the  present  treatment  to  those 
forms  of  energy  which  are  conveniently  imparted  to  air,  and  to 
those  forms  of  motors  which  utilize  the  expansive  force  incident 
to  such  heated  air.  References  to  discussions  of  other  media  will 
be  found  in  other  treatises  for  those  who  may  desire  to  pursue 
this  particular  department  more  fully.* 

6.  Sources  of  Heat  Energy. — In  seeking  for  a  source  of  heat 
energy  for  utilization  in  a  power-plant,  it  is  apparent  that  the 
same  sort  of  circumstances  must  govern.  The  source  of  heat 
must  be  conveniently  accessible,  cheap,  and  must  contain  large 
reserves  of  heat  in  a  small  bulk.  While  the  oxidation  of  all 
chemical  substances  is  accompanied  with  the  liberation  of  heat, 
there  are  certain  of  them  in  which  this  liberation  occurs  with  the 
most  convenient  rapidity.  These  substances  are  carbon  and  hydro- 
gen in  their  usual  natural  or  combined  forms.  These  occur  in 
nature  in  solid  form,  as  coal  or  wood ,  or  in  manufactured  coke  and 
charcoal;  in  liquid  form,  as  oils;  and  in  gaseous  form  either  natural 
or  manufactured.  It  will  be  apparent  in  the  later  treatment  that 
for  many  reasons  the  liberation  of  energy  by  the  combustion  or  oxi- 
dation of  gas  is  by  far  the  most  convenient,  so  far  as  the  motor  itself 
is  concerned  and  the  plant  as  a  whole.  It  may  be  desirable,  when 
the  fuel  is  in  solid  form,  to  convert  it  artificially  into  gas  by  a 
gas-making  process  and  use  it  in  that  form  rather  than  in  its 
natural  state.  For  the  purpose  of  this  treatise  the  source  of  heat 
will  be  taken  as  a  gas  and  its  process  of  liberation  will  be  the 
burning  of  this  gas  with  the  necessary  proportion  of  air  whereby 
the  energy  of  the  ignited  gas  is  imparted  to  raise  the  heat  energy 
of  the  air.  The  liquid  fuels  can  be  treated  and  considered  as 

*  See  Hutton's  "Heat  and  Heat  Engines,"  Chapters  IX  and  XXI. 


INTRODUCTORY.  ^ 

operating  in  a  manner  identical  with  that  of  gas,  inasmuch  as 
in  their  practical  utilization  the  liquid  fuel  is  injected  in  a  finely 
divided  state  into  the  air  and  is  ignited  in  this  vaporous  or 
atomized  condition,  when  it  behaves  exactly  as  the  gas  would, 
so  far  as  the  effect  in  liberating  energy  is  concerned. 

7.  Internal-combustion  Method  of  Heating  Air  as  a  Medium. 
—The  energy  liberated  from  a  gas,  or  an  oil,  or  a  solid  fire, 
by  its  combustion,  may  be  imparted  to  the  air  as  a  medium  by 
three  different  methods: 

I.  The  fire  may  be  placed  on  one  side  of  a  metallic  wall 
through  which  the  heat  of  the  fire  must  pass  to  heat  the  mass 
of  gas  on  the  other  side  of  the  wall.     This  plan  may  be  called 
the  external  heating  system.     It  is  the  method  used  in  the  steam- 
engine,  so  far  as  imparting  the  energy  of  the  fire  to  the  water 
and  steam  in  the  boiler  is  concerned,  and  is  the  method  which 
is  followed  in  the  ordinary  hot-air  engine  of  the  Ericsson  or 
similar  types. 

II.  The  second  method  is  that  whereby  a  solid  mass  heated 
by  the  fire  is  afterwards  removed  from  the  fire  and  brought  into 
contact  with  the  mass  of  gas  to  which,  by  contact  and  radiation, 
it  imparts  a  part  of  its  energy.  .  This  is  even  less  effective  than 
the  preceding  system,  but  may  be  called  a  combination  of  the 
external  and  internal  heating  systems. 

III.  The   third,  or   internal-combustion,   system  is  to  have 
the  fire  enclosed  in  a  vessel  and  maintained  in  activity  by  the 
mass  of  the  gas  itself,  which  receives  directly  and  without  an 
intervening  mass  the  heat  energy  from  that  fire.     In  this  case, 
obviously,  the  gas  must  be  such  as  to   furnish   the   necessary 
oxygen   for   this    internal    combustion,    and   of   course,    of   all, 
heated  air  is  the  most  convenient  for  this  class  of  operation. 

This  last  system,  the  internal-combustion  system,  is  by  far 
the  most  effective,  since  any  system  depending  upon  heating  air 
or  any  gas  by  contact  with  a  solid  at  a  high  temperature  must 
necessarily  be  slow;  it  requires  that  the  gas  be  in  thin  layers  or 
films,  and  large  masses  of  gas  have  to  be  handled  with  corre- 


8  THE   GAS-ENGINE. 

spending  bulk  or  weight  of  the  heating  surface.  For  effective 
transfer  the  hot  walls  must  be  hotter  than  the  receiving  medium, 
and  the  difference  of  temperature  must  be  so  great  that  it  is  diffi- 
cult to  find  a  material  for  the  solid  which  does  not  rapidly  dete- 
riorate from  the  high  heat. 

The  heating  of  the  medium  by  internal  combustion  has  been 
effected  either  with  coal,  with  oil,  or  with  gas.  The  methods 
used  might  be  tabulated  as  follows: 

I.  With  the  use  of  coal  as  a  source  of  heat. 

(a)  Air  is  passed  through  a  coal  fire  and,  after  having  effected 
the  combustion  of  the  coal  and  become  heated,  the  air  passes  to  the 
working  cylinder  of  the  motor,  where  it  exerts  its  expansive  force. 
The  names  connected  with  this  system  are  Cayley,  Genty,  Shaw. 

(b)  A  coal  fire  is  moved  through  an  enclosed  mass  of  air. 
(System  of  Lord.) 

II.  Using  a   liquid   fuel  not   vaporized   before   entering  the 
cylinder  of  the  motor. 

(c)  The  enclosed  air  in  the  motor  behind  the  piston  acts  as 
a  quiet  atmosphere  supporting  the  combustion  of  a  jet  of  oil. 
(Diesel.) 

(d)  The  air  is  caused  to  move  past  a  burner  and  in  passing 
it  supports  the  piston  and  the  heated  products  pass  on.     (Wil- 
cox,  Bray  ton,  Nordberg  &  Shadall.) 

(e)  Oil  is  forced  by  a  pump  into  a  hot  chamber  vaporized 
therein  by  the  heat  and  is  then  brought  into  contact  with  the  air. 
The  proportions  of  fuel  and  air  are  so  maintained  as  to  make 
the  resulting  gaseous  mixture  practically  explosive,  so  that  the 
combustion  propagates  itself  through  the  mixture.     (Hornsby, 
Capitaine,  Mietz  &  Weiss.) 

III.  Using  gas  or  oil  which  has  been  previously  vaporized. 
(/)  An  enclosed  mass  of  atmospheric  air  supports  the  com- 
bustion of  a  quiet  jet  of  gas-flame.     (Diesel  and  Gibbs.) 

(g)  Air  in  motion  passes  a  fixed  gas-flame  and  becomes  heated 
by  it.  This  is  the  method  of  most  of  the  atmospheric  engines, 
such  as  Wilcox,  Weiss,  and  the  Otto  Atmospheric. 


INTRODUCTORY.  $ 

(h)  Air  mixed  with  gas  in  explosive  proportions  is  caused  to 
pass  a  point  where  combustion  is  localized.  (Brayton,  Schmid, 
and  Beckfeld  and  Reeve.) 

(i)  Air  mixed  with  gas  in  such  proportions  that  a  flame  will 
propagate  itself  throughout  the  mass  is  enclosed  in  a  chamber 
and  while  at  rest  is  inflamed  by  being  locally  ignited.  To  this 
class  belong  the  Otto,  Priestman,  Nash,  Westinghouse,  and  nearly 
all  existing  internal-combustion  engines. 

The  present  treatment  will  confine  itself  to  the  systems  using 
oil  or  gas,  by  reason  of  the  fact  that  where  solid  fuel  is  used  the 
presence  of  corrosive  products  of  combustion  from  solid  fuel  and 
the  injury  to  the  cylinder  and  moving  parts  by  the  dust  and  ashes 
from  such  fuel  have  removed  engines  of  this  type  from  competi- 
tion with  those  using  the  more  convenient  form  of  the  fuel.  System 
i  includes  the  engines  which  may  properly  be  called  "explosive" 
engines,  since  a  flame  at  one  point  of  the  mixture  is  expected  to 
propagate  itself  throughout  it.  Those  in  system  h  are  properly 
"  non-explosive,"  since  the  combustion  is  localized  and  the  gases 
are  in  motion  when  heated.  Engines  in  this  latter  class  may  be 
continuous  non-explosive  (Reeve)  or  intermittent  non-explosive 
(Diesel). 

7a.  Analysis  of  the  Internal  Combustion  Motor.  —  It  would 
appear  therefore  that  the  modern  type  of  internal  combus- 
tion motor  is  designed  to  receive  the  energy  resident  in  a  gas 
or  liquid  fuel  into  its  cylinder,  and  there,  by  the  processes  of 
chemistry  and  the  laws  of  mechanics,  to  transform  that  heat 
energy  into  mechanical  work.  The  change  from  potential 
energy  in  the  fuel  into  actual  and  available  energy  is  effected  by 
the  combustion  process  to  be  discussed  in  the  next  chapter, 
whereby  the  heat  energy  which  is  a  necessary  accompaniment  of 
the  chemical  reaction  is  imparted  to  the  air  which  supports  it. 
From  the  cylinder  the  mechanical  energy  is  transmitted  by  a  re- 
volving shaft  to  the  point  where  work  is  to  be  done.  A  diagram 
is  subjoined  (Fig.  224)  which  will  illustrate  the  sources  of  energy 
as  input  which  must  be  supplied  to  such  a  motor  when  self-con- 
tained and  will  show  also  the  directions  of  output  of  mechanical 


io  THE  GAS-ENGINE. 

energy  for  the  motor  itself  as  well  as  for  useful  industrial  work. 
If  the  motor  is  not  self-contained,  some  of  these  sources  of 
energy  are  independent  of  it,  but  must  then  usually  be  paid  for 
in  other  units  than  those  of  heat  and  power. 

The  efficiency  of  such  a  motor  is  the  fraction  which  expresses 
the  relation  of  the  output  as  numerator  to  the  input  as  denomi- 
nator. If  both  be  expressed  in  heat  units,  the  fraction  is  the 
thermal  efficiency.  The  mechanical  efficiency  is  the  relation 
between  the  work  in  foot-pounds  delivered  to  the  piston  and 
the  work  delivered  from  the  revolving  crank-shaft. 


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IT 


CHAPTER  II. 

LIBERATION  OF  HEAT   ENERGY. 
COMBUSTION. 

8.  Introductory. — It  has  been  observed    in    the    preceding 
chapter   that    the   convenient    and    accessible    sources    for   the 
energy  due  to  heat  compelled  the  engineer  to  have  recourse  to 
the  combustion  of  the  elements  carbon  and  hydrogen  in  the  oxygen 
of  the  atmospheric  air.    While  heat  appears  as  a  transformation 
of  mechanical  energy  in  friction,  impact,  abrasion,  attrition,  and 
in  overcoming  electrical  resistances,  these  sources  are  excluded 
when  the  object  sought  is  heat,  which  may  itself  be  transformed 
into  mechanical  energy.     The  hydrogen  and  carbon  are  stored  in 
the  earth  as  the  result  of  processes  of  creation  and  distillation 
under  conditions  of  heat  and  pressure  in  geological  periods.     In 
order  that  this  energy  may  be  released  and  made  available  in 
practice,  conditions  favorable  to  the  necessary  rapid  oxidation 
must  be  established.     This  process  of  rapid  oxidation,  accom- 
panied with  the  liberation  of  heat  and  light,  is  called  combustion. 
While  oxygen  combines  with  many  of  the  metals  or  bases  or 
elements,  as  well  as  with  carbon  and  hydrogen,  and  such  processes 
are  also  properly  called  combustion,  yet  such  combinations  are 
either  too  costly  to  serve  as  convenient  sources  for  heat,  or  else 
the  process  of  oxidation  is  so  slow  that  sufficient  heat  cannot  be 
derived  from  the  process  in  any  practicably  short  or  momentary 
length  of  time. 

9.  Combustion.     Flame.     Smoke.     Incomplete  Combustion. 
— -Combustion  may  therefore,  for  the  purpose  in  hand,  be  denned 
as  a  combination  with  oxygen  which  takes  place  with  sufficient 
rapidity  to  be  accompanied  by  the  phenomena  of  light  and  heat 


LIBERATION  OF  HEAT  ENERGY.  13 

In  the  combustion  of  a  solid  fuel  it  appears  to  be  necessary  to 
raise  the  surface  of  the  solid  particles  of  that  fuel  to  a  tempera- 
ture at  which  the  carbon  and  hydrogen  which  it  contains  shall  be 
distilled  on  that  surface  and  form  into  a  gas;  in  other  words,  the 
oxygen  of  the  air  cannot  unite  with  a  solid,  but  that  solid  must 
first  be  gasified  before  chemical  combination  can  begin.  Simi- 
larly with  a  liquid  fuel  it  must  either  be  so  finely  divided  as  to 
be  a  mist  or  to  constitute  an  atmosphere  loaded  with  a  vapor  of 
combustible  material.  Even  then  the  gas  must  be  raised  to  a 
temperature  of  ignition,  in  order  that  combustion  may  begin. 

The  term  fire  came  into  use  before  the  combustion  of  gas  was 
general  or  recognized,  and  is  therefore  properly  restricted  to  the 
continuous  process  of  chemical  union  of  a  combustible  with  oxygen 
by  distillation  from  a  solid  such  as  wood  or  coal,  or  their  deriva- 
tives. When  there  is  no  solid  there  is  flame  but  not  a  fire. 
There  may  be  fire  without  flame;  but  if  the  gas  or  atomized  fuel 
supply  were  shut  off  and  the  flame  disappeared  and  there  were 
no  embers  or  clinkers  or  ash  left  behind,  which  are  necessarily 
associated  with  the  idea  of  quenching  a  fire,  then  there  was  no 
fire  although  there  was  flame.  The  flame  at  the  wick  of  an  oil 
lamp-burner  or  at  a  gas-burner  is  not  a  fire,  but  the  flame  of  a 
burning  match  or  in  burning  shavings  or  waste  is  one.  The 
extinction  of  a  flame  is  practically  an  instantaneous  process 
when  the  arrest  of  gas-flow  can  be:  the  extinction  of  a  fire  is 
always  a  gradual  and  progressive  process.  The  electric  spark 
is  not  a  fire  nor  a  flame,  but  like  the  flame  it  can  start  the  chemi- 
cal processes  for  which  heat  is  requisite,  and  produce  the  same 
results  as  a  true  fire. 

A  luminous  flame  is  a  current  of  hot  gas  carrying  with  it  solid 
particles  at  such  a  temperature  as  to  glow  or  give  out  heat  and 
Light.  These  solid  particles  may  be  combustible  or  they  may  be 
mechanically  suspended  in  the  gas  and  glowing,  but  inert  so  far 
as  the  generation  of  heat  is  concerned.  When  these  particles  are 
combustible  and  the  temperature  of  the  current  is  sufficiently 
high  they  will  glow  and  burn  until  they  become  entirely  gas,  and 
disappear.  In  the  absence  of  solid  particles,  a  current  of  hot  gas 
the  resu1t  of  complete  union  with  oxygen  which  would  be  called 


14  THE  G4S-ENG1NE. 

complete  com1 ustion,  would  be  colorless  and  invisible.  Such  a 
flame  is  called  a  non-luminous  one.  The  temperature  of  the 
current  of  flame  is  measured  by  the  degree  of  incandescence  of 
these  particles.  When  they  are  intensely  white  they  are  in  their 
hottest  condition.  A  yellow  flame  is  cooler,  and  a  red  flame  is 
still  cooler.  A  flame  usually  results  when  the  supply  of  oxygen 
at  the  point  where  combustion  began  was  not  quite  sufficient,  or 
the  temperature  not  sufficiently  elevated  to  produce  a  complete 
combustion  of  the  fuel  at  the  point  where  such  combination 
began.  A  luminous  flame  is  much  the  most  efficient  means  of 
heating  a  solid  by  radiation.  The  complete  combustion  in  the 
necessary  mass  of  air  produces  the  highest  possible  temperature 
at  the  time  and  place  of  such  union,  and  is  most  effective  for  heat- 
ing a  body  immersed  in  the  current  of  non-luminous  gas. 

The  word  incandescence  strictly  used  refers  to  a  condition 
of  heat  accompanied  by  light  as  an  evidence  of  great  heat  energy, 
but  without  chemical  action.  The  word  incandescence,  how- 
ever, is  often  extended  to  include  the  condition  in  which  the  chem- 
ical action  is  relatively  slow  while  the  heat  intensity  is  high. 

Smoke  is  a  current  of  hot  gas  carrying  with  it  solid  particles 
of  carbon  which  are  not  hot  enough  to  ignite  and  burn,  or  which 
have  been  cooled  below  the  temperature  required  for  such  com- 
bustion. The  term  smoke  is  often  applied  to  currents  of  gas 
carrying  with  them  tarry  or  other  matter  in  a  finely  divided  state. 
Such  a  current  has  all  the  appearance  of  a  smoke,  but  differs  from 
it,  inasmuch  as,  if  it  were  brought  up  to  a  sufficient  temperature, 
it  would  ignite  and  burn.  A  true  smoke,  carrying  particles  of 
lampblack,  cannot  be  so  treated,  since  the  lampblack  is  only 
capable  of  ignition  at  temperatures  considerably  above  those 
which  can  be  brought  about  except  in  the  electrical  arc  or  with 
the  oxyhydrogen  blowpipe.  These  conditions  make  it  apparent 
that  to  prevent  smoke  is  the  best  that  the  engineer  can  do,  and 
that  there  is  no  such  thing  as  smoke  consumption.  It  is  one  great 
advantage  of  the  combustion  of  gas  and  finely  divided  oil,  that 
the  conditions  of  smokeless  combustion  are  much  more  easily 
attained  than  with  the  combustion  of  solids.  The  gas  does  not 


LIBERATION  OF  HEAT  ENERGY.  15 

require  distillation  by  heat  and  there  are  no  solid  particles  in 
a  gas  which  is  a  true  chemical  mixture.  In  the  combustion  of 
such  a  gas  it  will  happen  that  not  infrequently  with  an  inade- 
quate supply  of  oxygen  and  too  low  a  temperature  the  carbon 
will  separate  in  the  form  of  soot  or  lampblack.  Thorough 
mixture  of  the  gas  and  oxygen  and  high  temperature  will 
diminish  this  difficulty  from  the  deposition  of  carbon. 

Incomplete  combustion  is  the  union  of  carbon  with  oxygen 
to  form  a  compound  which  upon  combination  with  the  necessary 
additional  oxygen  in  the  presence  of  heat  will  burn  to  the  final 
state  in  which  the  products  of  such  combustion  are  incom- 
bustible. 

The  usual  form  of  this  incomplete  combustion  is  the  burning 
of  carbon  to  carbon  monoxide  (CO),  which  will  burn  to  carbon 
dioxide  or  carbonic  acid  (CO2)  upon  the  supply  of  the  necessary 
additional  oxygen  and  heat.  If  the  carbon  escapes  from  the 
apparatus  in  use  without  being  completely  burned,  there  is, 
obviously,  a  loss  of  available  energy. 

10.  Ignition.  Explosion.  Propagation  of  Flame.  —  In 
order  that  the  gas  distilled  from  the  solid  fuel  or  derived  from 
any  source  should  begin  its  combination  with  oxygen  it  is  neces- 
sary that  it  should  be  set  fire  to.  This  means  that  the  mixture 
of  oxygen  and  gas,  or  either  in  the  presence  of  the  other,  shall  be 
raised  to  a  temperature  at  which  chemical  combination  shall  be 
possible.  This  beginning  of  chemical  union  is  called  ignition 
and  can  usually  be  effected  most  conveniently  by  bringing  a 
flame  or  an  incandescent  solid  into  contact  with  the  mixture 
whereby  a  part  of  it  shall  be  raised  to  the  temperature  required. 
The  passage  of  an  electrical  spark  through  the  mixture  will  effect 
this  ignition  also.  If  the  mixture  is  sufficiently  intimate  and  in 
proper  proportions,  the  ignition,  beginning  at  one  point  by  flame 
or  spark  or  incandescence,  will  propagate  itself  through  the  mass 
and  the  entire  mixture  will  become  ignited.  If  the  mixture  is 
not  intimate  and  there  is  not  the  proper  amount  of  oxygen,  or 


1 6  THE  GAS  ENGINE. 

if  the  temperature  of  the  flame  is  low  by  reason  of  the  poor  quality 
of  the  gas,  the  flame  may  not  propagate  itself  through  the  entire 
mass  and  the  combustion  will  be  incomplete. 

If,  on  the  other  hand,  the  mixture  be  rich  in  combustible, 
the  propagation  of  the  chemical  combination  through  the  mass 
may  be  so  rapid  as  to  be  practically  instantaneous.  When  this 
occurs  the  expansion  of  the  volume  of  the  mixture  due  to  this 
rapid  combustion  will  occur  with  a  suddenness  which  makes  it 
concussive,  and  such  an  ignition  or  propagation  of  the  ignition 
through  the  mass  is  called  an  explosion.  The  noise  which  is 
commonly  attached  to  an  explosion  is  a  secondary  phenomenon 
resulting  from  the  concussive  character  of  the  expansion  of  the 
heated  mass.  It  may  either  be  an  impact  of  the  air,  as  in  the 
case  of  a  powerful  electrical  discharge  among  the  clouds,  or  it 
may  be  the  reaction  of  forces  in  a  solid  mass,  as  in  the  detonation 
of  rock  disrupted  by  explosives.  An  explosive  is  a  solid  or  liquid 
having  this  property  of  intensely  rapid  propagation  of  its  ignition 
coupled  with  a  copious  supply  from  itself  of  the  necessary  oxygen 
for  the  required  chemical  combination  to  take  place  without  draw- 
ing that  oxygen  at  the  slow  rate  which  would  occur  when  the 
oxygen  was  furnished  by  the  air. 

When  the  problem  of  ignition  is  applied  to  a  gaseous  fuel, 
it  will  appear  that  there  are  several  ways  in  which  the  gas  and 
the  oxygen  may  be  brought  together  for  ignition  and  combustion, 
and  that  each  method  may  constitute  a  class. 

Class  I.  Gas  issuing  from  an  orifice  into  a  supporting  at- 
mosphere and  where  all  the  oxygen  for  combustion  is  derived 
from  that  atmosphere. 

This  first  class  of  combustion  is  very  imperfect,  so  that  only 
low  temperatures  result,  while  large  excesses  of  oxygen  are  re- 
quired- over  what  is  chemically  necessary.  It  is  this  very  im- 
perfection which  causes  the  efficiency  of  the  ordinary  gas-jet 
as  a  source  of  light.  The  unequal  distances  travelled  by  mole- 
cules of  gas  before  reaching  the  place  where  they  can  find  and 
combine  with  the  necessary  oxygen  gives  the  flame  a  volume, 
i.e.,  a  certain  portion  of  space  is  filled  with  the  flame.  In  the 


LIBERATION  OF  HEAT  ENERGY.  17 

study  of  combustion,  as  the  origin  of  heat,  this  class  is  of  no 
importance. 

Class  II.  Gas  mixed  with  oxygen  insufficient  in  quantity  for 
its  combustion  or  for  the  formation  of  an  explosive  mixture, 
issuing  into  a  supporting  medium  from  which  all  necessary  addi- 
tional oxygen  is  derived. 

Mixing  the  oxygen  with  the  gas,  previously  to  heating  for 
ignition,  as  in  Class  II,  is  a  direct  aid  to  nature,  eliminating  the 
hunting  process  of  Class  I,  or,  at  any  rate,  reducing  it,  and  making 
necessary  only  the  heating  to  the  ignition  temperature  to  cause 
combustion.  This  is  shown  in  the  immediate  shortening  of  the 
flame  over  that  of  the  previous  class,  and  its  loss  of  luminosity, 
while  still  retaining  the  volume  character  of  the  flame.  It  is 
the  principle  of  the  Bunsen  burner,  and  the  large  class  of  appa- 
ratus which  follow  it  for  use  in  furnaces,  heaters,  cooking-stoves, 
and  for  heating  water  in  steam-carriages. 

In  most  of  these  the  mixture  of  air  with  the  fuel  is  made  by 
causing  a  jet  of  gas  to  impinge  on  a  mass  of  air,  some  of  which 
is  carried  along  with  the  air  under  the  double  influence  of  gas 
friction  and  the  heated  top  of  the  burner,  whence  the  mixture 
issues. 

Combustion  of  Class  II  is  characterized  by  the  fact  that 
there  is  an  actual  volume  of  flame;  the  flame  is  hotter  than  in 
Class  I,  which  means  that  for  a  given  flame  volume  either  more 
gas  is  burned  or  the  products  of  combustion  are  less  diluted; 
the  flame  is  less  luminous  and  not  of  uniform  color  throughout 
its  volume. 

An  infinite  variety  of  details  of  arrangement  in  the  exit  and 
mixing  of  the  air  and  gas  may  be  devised  with  varying  results 
for  special  cases,  but  it  is  true  of  all  of  them  that,  though  the 
combustion  be  very  perfect  and  the  amount  of  heat  generated 
large,  yet  there  is  always  a  "flame  volume,"  indicating  a  struggle, 
as  it  were,  on  the  part  of  the  gas  and  air  in  their  final  combus- 
tion. The  combustion,  though  approaching  perfection  in  many 
cases,  is  rendered  so  only  by  the  use  of  a  large  excess  of  the 


1 8  THE  GAS-ENGINE. 

oxygen  chemically  required  giving  oxidizing  products  of  com- 
bustion. 

Class  III.  Gas  mixed  with  oxygen  in  quantities  insufficient 
for  complete  combustion,  but  sufficient  for  the  formation  of  an 
explosive  mixture,  issuing  from  an  orifice  into  a  supporting 
atmosphere,  from  which  all  necessary  additional  oxygen  is  to  be 
derived. 

Class  IV.  Gas  mixed  with  oxygen  in  just  sufficient  quantities 
for  combustion,  issuing  from  an  orifice  into  any  sort  of  atmos- 
phere. This  sort  of  mixture  may  be  called  a  " chemical"  mix- 
ture. 

Class  V.  Gas  mixed  with  oxygen  in  such  quantities ,  as  to 
form  an  explosive  mixture,  but  with  insufficient  oxygen  for  com- 
plete combustion,  burned  in  a  mass  by  a  single  explosion.  - 

Class  VI.  Gas  mixed  with  oxygen  in  chemical  proportions, 
burned  by  a  single  explosion  in  mass; 

It  is  only  when  the  gas  and  air  are  previously  mixed  com- 
pletely and  uniformly  in  the  proper  chemical  proportions 
that  non- reducing,  non-oxidizing  products  of  combustion  are 
obtained,  and,  since  none  of  the  heat  goes  to  warm  excesses 
of  oxygen  or  of  fuel,  the  temperature  of  these  products  must  be 
the  highest  possible.  Combustion  of  this  sort  is  flameless,  or, 
rather,  what  flame  there  is  is  without  volume,  having  only  length 
and  breadth  without  thickness,  and  is,  in  fact,  a  surface. 

Such  combustion  is  governed  by  laws  quite  different  from 
those  under  which  the  classes  already  noted  operate,  and  it  is 
to  the  combustion  of  chemical  and  other  explosive  mixtures 
that  attention  may  for  the  present  be  mainly  devoted. 

Consider  first  the  class  mentioned  as  Class  VI,  in  which  a 
mass  of  chemical  mixture — i.e.,  gas  and  its  needed  oxygen- 
is  confined  in  a  chamber.  If  inflammation  be  provoked  at  any 
point  of  the  mass,  it  will,  by  self-propagation,  finally  and  suc- 
cessively inflame  the  whole  mass.  This  is  the  first  and  funda- 
mental principle  of  this  sort  of  combustion.  The  investigation 
of  this  propagation  of  inflammation  by  such  men  as  Davy,  Bun- 


LIBERATION  OF  HEAT  ENERGY.  19 

sen,  Mallard  and  LeChatelier,  Berthelot,  and  others  has  shown 
that-: 

(a)  In  any  mixture  the  rate  of  propagation  is  constant  for  a 
given  temperature  before  inflammation. 

(b)  The  rate  of  propagation  for  such  mixtures  varies  with 
different  combustibles,  being,  for  example,  very  fast  for  hydro- 
gen and  slow  for  marsh-gas. 

(c)  The  rate  of  propagation  increases  with  the  temperature  of 
the  mixture  before  inflammation. 

(d)  The  combustion  is  visible  by  reason  of  a  flame-cap,  or 
deep-blue  film   of  flame,  which   travels  through  the  mass,  and 
which,  at  any  instant,  completely  separates  all  the  burned  from 
the  unburned  mixture. 

This  uniformity  of  velocity  of  inflammation  would  indicate 
that  in  a  mass  where  inflammation  had  started  at  a  point,  the 
flame-cap,  or  surface  of  combustion,  exists  at  any  instant  on  the 
surface  of  a  sphere  whose  radius  is  proportional  to  the  time 
elapsed. 

All  this  has  been  assumed  so  far  to  take  place  in  a  large  mass  of 
gas.  If,  however,  the  enclosing  vessel  be  given  special  forms, 
certain  other  characteristics  are  brought  out.  One  which  is  of 
interest  is  the  fact  that,  when  the  enclosing  vessel  is  a  cylinder, 
or  prism,  in  which  the  combustion  surface  travels  with  its  centre 
on  the  axis,  the  velocity  becomes  affected  by  reduction  of  cross- 
section,  and  that  there  will  always  exist  for  every  such  mixture 
an  area  of  cross-section  so  small  that  the  self-propagation  ceases. 
This  has  been  explained  by  saying  that  the  walls  carried  off 
heat  so  fast  that  the  small  flame- cap  •  could  not  generate  heat 
enough  to  keep  itself  above  the  temperature  of  ignition.  Davy 
secured  the  same  effect  by  using  his  screen  of  wire  gauze,  which, 
if  interposed  in  the  path  of  the  combustion  surface,  instantly 
cooled  the  same  sufficiently  to  prevent  the  ignition  of  the  mixture 
on  the  other  side,  provided,  of  course,  the  temperature  of  the 
gauze  itself  is  sufficiently  low. 

When  a  neutral  diluent  gas,  such  as  N  or  CO2,  is  added 
to  a  chemical  mixture  arranged  for  the  above-discussed  com- 


20  THE  G4S-ENGINE. 

bustion,  its  effect  is  to  reduce  the  rate  of  propagation,  though 
not  in  conformity  with  any  law  yet  discovered.  Of  course  there 
will  be  a  point  when  so  much  of  the  neutral  gas  is  present  that 
combustion  is  impossible,  but  no  reliable  data  are  at  hand  on 
this  point,  and  the  same  conditions  often  give  widely  varying 
results. 

While  large  quantities  of  a  neutral  gas  may  be  added,  with- 
out affecting  the  combustion  except  to  decrease  the  rate  of  prop- 
agation, a  dilution  by  a  comparatively  slight  amount  of  oxygen 
will  prevent  it  altogether.  An  excess  of  gas,  it  has  been  found, 
will  act  within  certain  limits  like  the  presence  of  a  neutral  gas. 
By  far  larger  amounts  of  fuel  than  of  oxygen  may  be  present  in 
excess  without  arresting  combustion. 

In  Class  V,  where  explosive  mixtures  are  burned  in  mass, 
the  mixtures  having  excess  of  fuel,  the  combustion  is  possible 
within  quite  wide  limits,  with  no  other  effect  than  varying  the  rate 
of  propagation.  In  fact,  a  great  deal  of  it  appears  to-day  in 
gas-engines  which  run  on  the  richer  fuels.  While,  of  course,  in 
these  engines  the  proper  chemical  mixture  should  be  invariably 
used  with  only  sufficient  dilution  to  secure  a  proper  mechanical 
mixture,  they  are  seldom,  if  ever,  constructed  to  maintain  this 
properly,  and,  as  a  slight  excess  of  oxygen  beyond  this  relation 
will  completely  prevent  inflammation,  the  error  is  always  made 
on  the  other  side;  sooty  exhausts  bear  testimony  to  this.  The 
gas-engine  also  gives  evidence  of  the  fact  that  neutral  gases 
decrease  the  rate  of  propagation,  for  in  some  two-cycle  engines 
it  is  impossible  to  get  a  vertical  combustion  line  on  the  indicator- 
diagram  with  a  fixed  ignition,  except  at  very  slow  speeds — about 
50  revolutions  per  minute.  This  is  due  entirely  to  the  presence 
of  exhaust-gases  in  excessive  quantities  as  diluents  to  the  charge. 

Some  of  the  principles  above  noted  as  belonging  to  masses  of 
mixture  at  rest  will  make  clearer  the  nature  of  the  problem  of 
combustion  of  the  same  mixtures  when  in  motion  issuing  from 
an  orifice. 

It  has  been  found  in  this  latter  case  that  a  mixture  of  gas  and  air 
in  proportions  which  would  be  explosive  if  it  were  quiescent  in 


UN!VERS!TY| 


LIBERATION  OF  HEAT  ENERGY.  21 

a  chamber  can  be  burned  with  perfect  safety  from  a  nozzle, 
provided  the  rate  of  outflow  of  the  mixture  from  that  nozzle 
is  slightly  in  excess  of  the  rate  at  which  propagation  of  the  flame 
would  occur  in  that  mixture.  A  cap  of  flame  forms  at  a  distance 
from  the  nozzle  which  will  vary  with  the  velocity  of  efflux. 
When  that  velocity  of  efflux  exceeds  the  rate  of  propagation,  the 
flame  will  retreat  farther  and  farther  from  the  nozzle  until  it 
becomes  extinguished  by  the  lowering  of  temperature  due  to 
the  surrounding  medium.  The  flame  has  blown  itself  out.  On 
the  other  hand,  if  the  velocity  of  efflux  decreases,  the  flame  will 
approach  the  nozzle,  and  if  it  is  allowed  to  fall  sufficiently,  the 
flame  will  run  back  into  the  nozzle  itself  and  thus  back  into  the 
stationary  mixture  in  the  containing  vessel,  which  will,  by  the 
propagation  property  which  it  possesses,  result  in  an  explosion. 
Some  further  facts  on  the  treatment  of  this  class  of  combustion 
will  be  presented  in  Chapter  XIX. 

SPONTANEOUS  COMBUSTION  is  a  phenomenon  which  has  been 
(bserved  where  the  absorption  of  oxygen  by  a  body  of  porous 
character  may  become  sufficiently  rapid  so  that  the  temperature 
due  to  this  chemical  combination  shall  raise  the  combustible 
up  to  the  point  at  which  flaming  will  begin.  It  were  better  if 
this  action  were  called  spontaneous  ignition.  The  conditions 
favorable  for  it  are  the  presence  of  a  readily  oxidizable  body, 
distributed  in  a  finely  divided  state  over  or  through  some  material 
whereby  a  great  surface  is  exposed  to  action  by  oxygen.  Oily 
rags  and  greasy  cotton  waste  fill  these  conditions,  and  both  are 
particularly  liable  to  spontaneous  ignition.  If  the  heat  of  oxida- 
tion can  be  conducted  off  as  fast  as  it  is  generated,  spontaneous 
ignition  is  less  likely  to  occur,  but  as  a  rule  the  porosity  which 
exposes  a  large  surface  to  oxidation  is  unfavorable  to  the  transfer 
of  the  heat.  Capillary  action  may  also  act  to  help  the  rapid 
oxidation  process. 

ii.  Oxygen  and  Air  Required  for  Combustion.  Air  Re- 
quired for  Combustion  of  Carbon.  —  Since  combustion  is  the 
chemical  union  of  oxygen  with  the  combustible  elements,  it  must 
take  place  according  to  the  laws  of  chemical  combinations,  and 


22  '  THE  GAS-ENGINE. 

the  weights  of  air  for  each  element  will  be  those  which  will  furnish 
the  oxygen  weight  demanded  by  the  relations  of  the  atomic 
weights  in  the  chemical  compounds  which  are  formed. 

Atmospheric  air  contains  oxygen  and  nitrogen  in  the  follow- 
iny  proportions,  at  a  temperature  of  melting  ice : 

By  Weight. 

Oxygen o .  236 

Nitrogen o .  764 


i  .  ooo  i  .  ooo 


Whence  a  given  quantity  of  air  weighs  ^W  =  4-25  times  the 
weight  of  the  oxygen  which  it  contains,  and  -*•>?££•  =  1.31  times 
the  weight  of  the  nitrogen  which  it  contains. 

By  volume  a  given  quantity  of  air  will  occupy  J]npTL  =  4»69 
times  the  volume  of  the  oxygen  which  it  contains,  and  -V°WL=  J-27 
times  the  volume  of  the  nitrogen  which  it  contains.  At  62°-64° 
Fahr.,  where  computations  are  usually  made,  this  multiplies  to 
replace  oxygen  by  atmospheric  air  becomes  475-480,  and  this 
value  is  used  in  computing  the  tables. 

When  carbon  burns  to  carbonic  acid,  which  is  the  normal  and 
preferred  combustion  process,  the  chemical  equation  for  the 
process  and  result  is 

C+02  =  C02, 

12+32=44, 

in  which  C  is  the  symbol  for  one  part  by  weight  of  carbon;  O2 
is  the  symbol  for  the  two  parts  of  oxygen  required  to  burn  the 
carbon  to  carbonic  acid,  whose  symbol  is  CO2.  The  figures 
below  each  are  the  respective  multiples  of  their  atomic  weights 
for  combination  ;  whence  it  appears  that  the  oxygen  weight  needed 
will  be  given  by  the  proportion 

Weight  of  oxygen  )   m  (  Weight  of  carbon  j  .        .  I2 
required          )  '  (        furnished      .    } 

or  2.66  pounds  of  oxygen  must  be  furnished  to  burn  the  one  pound 
of  carbon  completely.  The  weight  of  the  carbonic  acid,  CO2, 


LIBERATION  OF  HEAT  ENERGY.  23 

will  be  the  sum  of  the  weights  of  carbon  and  oxygen,  or  1  +  2.66 
=  3.66  Ibs. 

When  the  combustion  is  effected  by  supplying  atmospheric 
air,  there  must  be  supplied  from  the  foregoing  calculation  con- 
cerning atmospheric  air  2.66X4.25  =  11.3  Ibs.  of  air.  Add 
i.o  Ibs.  of  carbon.  The  products  of  the  combustion  will  weigh 
12.3  Ibs.  and  will  consist  of  carbonic  acid  and  nitrogen. 

Similarly,  the  volume  of  air  in  cubic  feet  to  burn  one  pound 
of  carbon  can  be  calculated  from  the  weight  of  it.  At  atmos- 
pheric pressure  and  at  the  temperature  of  melting  ice  a  pound 
of  air  occupies  12.39  cubic  feet.  Hence  11.3  pounds  of  air  will 
occupy  11.3X12.39=140  cubic  feet  at  32°  F.,  or  152  cubic  feet 
at  62°  F. 

When  carbon  (C)  burns  to  carbonic  oxide  (CO)  instead  of 
to  carbonic  acid  (CO2), 

c+o=co, 

12+16=28, 

whence  the  oxygen  is  jf  of  the  unit  weight  of  the  carbon,  and 
1.33  pounds  of  oxygen  or  1.33X4.25  =  5.65  pounds  of  air  are 
required.  The  products  of  the  combustion  are  2.33  pounds  of 
carbonic  oxide.  The  weight  of  air  for  this  combustion  will  be 
1.33X4.25  =  5.65  pounds  of  air,  or  5.65X12.39=70  cubic  feet 
of  air  at  32°  F.,  or  76  at  62°  F. 

If  the  CO  burns  as  a  combustible  gas  to  CO2,  the  additional 
supply  of  air  is  required  as  in  the  preceding  case. 

12.  Air  Required  for  Combustion  of  Hydrogen. — Hydrogen 
burns  to  water-vapor  or  steam-gas,  whose  chemical  symbol  is 
H2O.  The  chemical  equation  is 

H2+0=H20, 

2+16  =  18, 

whence  one  pound  of  hydrogen  requires  -/ =  8  pounds  of  oxygen, 
and  8+1  =  9  pounds  of  water- vapor  result  as  products  of  the 
combustion,  if  oxygen  is  used  alone. 

Eight  pounds  of  oxygen  need  8X4.25  =  34  pounds  of  air, 
making  34+1  =  35  pounds  of  water  and  nitrogen  as  the  actual 


24  THE  G4S-ENGINE. 

weights  of  the  products  of  combustion.  The  volume  of  air  for 
hydrogen  combustion  is  34X12.39  =  421  cubic  feet  of  air  at 
32°  F.  or  457  cubic  feet  of  air  at  62°  F. 

13.  Air  Required  for  Combustion  of  Compounds. — In  the 
burning  of  compounds  of  carbon  and  hydrogen  each  acts  as 
though  the  other  did  not  exist,  and  the  air  required  is  the  sum  of 
the  requirements  of  the  constituents.  Marsh-gas,  for  instance, 
known  also  as  light  carburetted  hydrogen  or  methane,  of  com- 
position CH4,  requires 

C+O2  =  CO2      =12  +  32=44 
H4+02  =  2(H20)=  4+32  =  36 

Total  =  16  +  64  =  80 

The  added  oxygen  is  four  times  the  weight  of  the  original  gas, 
or  one  pound  of  gas  gives  five  pounds  of  carbonic  acid  and  water 
if  no  nitrogen  is  added.  Four  pounds  of  oxygen  will  be  furnished 
by  4X4.25  =  17  pounds  of  air  at  32°,  or  17X12.39  =  208  cubic 
feet  of  air  at  32°,  and  giving  18  pounds  of  CO2,  H2O,  and  N. 

The  proportions  of  the  CO2  and  H2O  were  respectively  |-£  of 
the  former  and  f  f  of  the  latter;  or  there  was  one  part  of  water 
to  1.32  parts  of  carbonic  acid,  since 

36  144  ::  i  :  1.22. 

Similarly,  for  olefiant  gas,  ethylene,  C2H4,  the  equations  will 
be 

C2+O4=2CO2  =  24+64=  88 
H4+02  =  2H20=  4+32=  36 

Total  =  28 +96  =124 

That  is,  for  a  weight  of  gas  (28)  will  be  required  a  weight  of 
oxygen  (96),  or  3.43  pounds  for  one  pound  of  gas,  making  4.43 
pounds   of   CO2   and   H2O,    and   calling   for   3.43  X 4.25  =  i4.5& 
pounds  of  air,  or  14.58X12.39=180  cubic  feet  of  air,  at  32°. 
The  products  of  combustion  will  be  14.58+1  =  15.58  pounds 


LIBERATION  OF  HEAT  ENERGY. 


of  CO2,  H2O,  and  N,  and  in  this  combustion  one  part  of  water 
goes  to  2.44  parts  cf  carbonic  acid. 

If  there  is  sulphur  enough  in  the  fuel  not  to  be  negligible, 
then  an  additional  chemical  equation  is  required  and  more  oxygen; 
S  burns  to  SO2,  or  32  +  32  =  64.  One  pound  of  oxygen  is  required 
for  each  pound  of  sulphur,  corresponding  to  4.25  pounds  of  air 
or  12.39X4.25  =  52.65  cubic  feet  of  air  at  32°  or  57  cubic  feet  at 
62°  F. 

Generalizing  from  the  foregoing,  it  would  appear  possible 
to  designate  hydrocarbon?  by  a  symbol  CMHm,  in  which  n  and  m 
shall  be  the  atoms  of  each  constituent  in  one  molecule.  Accept- 
ing the  generally  received  principles  of  the  chemists  that  equal 
volumes  of  all  gases  contain  the  same  number  of  molecules 
(Avogadro's  law),  and  that  each  molecule  is  made  up  of  twor 
atoms,  it  will  follow  that  the  molecules  of  oxygen  required  for 
one  molecule  of  the  hydrocarbon  will  be 


or  n+  —  volumes  of  oxygen  are  required  for  the  complete  com- 
4 

bustion  of  one  volume  of  the  hydrocarbon.     The  volum'e  of  air 
will  be  as  before 


-  X4-7S- 


Tabulating  some  of  these  results: 


Element  i  pound. 

Pounds  of 
Oxygen. 

Pounds  of 
Air. 

Volume  of 
Air  at  32°. 

Weight  of 
Products 
of  Com- 
bustion. 

Composition  of  the 
Products  of  Combustion. 

Hydrogen  

8 
2.66 
1-33 

4 

3-45 

i 

34 

«-3 

S-65 

J7 
14.58 
4.25 

421 
140 
70 

210 
1  80 

53 

35 
12.3 
6.6 

ii  | 

I5-6J 

5-25 

Water-vapor 
Carbon  dioxide 
Carbon  monoxide 
Carbon  dioxide 
Water-vapor 
Carbon  dioxide 
Water-vapor 
Sulphur  dioxide 

Carbon,  C  to  CO2 
C  to  CO  

CH4.  . 

C,H4  . 

Sulphur  

26 


THE  GAS-ENGINE. 


It  should  be  observed  that  the  volume  of  the  products  of  com- 
bustion must  involve  an  assumption  of  a  particular  temperature 
at  which  the  weight  per  cubic  foot  shall  be  known  for  the  mixture 
of  gases.  This  volume  and  temperature  being  known  and  called 
respectively  v0  and  TQ1  the  volume  i/,  at  the  temperature  Tl  will 
be 


the  pressure  being  supposed  to  be  the  same  in  both  states.  The 
following  table  gives  the  series  of  hydrocarbons  forming  the 
marsh-gas  group,  in  which  w  =  2W+2,  when  n  is  the  proportion 
of  carbon  in  any  constituent: 


I 

2 

3 

4 

5 

6 

Name  of  Gas  or  Liquid. 

Composi- 
tion by 
Atoms. 

Per  cent 
of  C. 

Per  cent 
of  H. 

Boi  ling- 
Point 
Fahr. 

Specific 
Gravity 

GASES. 

CH4 

75  .00 

25.00 

°-5'>9 

Ethane       .    .  .          

C2H6 

80.00 

20.00 

Propane  ......              .. 

C3H8 

81.81 

18.19 

Butane  .      .  .      ..        ........... 

QH10 

82.80 

17.20 

. 

0.6oo 

LIQUIDS. 
Pentane                                    -    - 

C.H,, 

8?  -z-i 

16  67 

86 

o  628 

Hexane                         ... 

C«H,, 

8?    72 

16  28 

ic.6 

o  664 

Heptane.                       .    .   .    .    _ 

cat 

wo-  1* 
84  oo 

16  oo 

X0" 

208 

o  660 

Octane     .               

cjfe 

84    21 

I^    70 

2C7 

O    7O3 

Nonane.  .        ........... 

CnH20 

84    ^8 

*3*/y 

ic;  62 

277 

O   74.1 

Decane.            ...    .    .    .    ...    ... 

r"»~3" 

84   c  i 

1^  .40 

••// 

^16 

O   7^7 

Endecane.   .    .    .....    ......... 

C.HM 

84.61 

1C  .  7Q 

160 

/o/ 
O.7O< 

Dodecane  

84.70 

J<  .  T.O 

S86 

w-/»^ 

0.776 

Tridecane 

f    T-T 

84.  78 

I  ^     22 

4.'>O 

O    7Q2 

Tetradecane 

84.  Sc. 

I  C     j  C. 

462 

Pentadecane 

C.H,, 

<-"*-":> 
84.  oo 

I  ^    TO 

4O7 

Hekdecane               .            .    . 

C  H 

84    Q4. 

I?    06 

^^6 

Octodecane  . 

8^  04 

*5-w 

14  .OO 

SOLIDS. 
Paraffin  (myricyl).  .  ............ 

8=5.26 

14-74 

Paraffin  (ceryl) 

gC     71 

14.   60 

600 

14.  Combustion  of  an  Analyzed  Fuel.  Combustion  Ratio. 
— The  chemical  analysis  of  a  fuel  gives  the  percentage  or  weight 
of  C,  H,  S,  and  O  in  a  pound,  or  the  proportion  in  a  cubic  foot. 


LIBERATION  OF  HEAT  ENERGY.  27 

Hence  the  calculation  for  the  weight  or  volume  of  air  is  identical 
with  the  foregoing,  except  by  reason  of  the  provision  for  satisfy- 
ing the  oxygen  in  the  fuel  itself.  The  investigations  of  Dulong 
and  Despretz  and  others  have  shown  the  principle  to  hold,  that 
when  oxygen  and  hydrogen  exist  in  a  compound  in  the  proper 
proportions  to  form  water  by  union  with  each  other,  these  con- 
stituents have  no  effect  either  in  affecting  the  calorific  power  or 
the  demand  for  outside  oxygen  for  combustion.  It  is  only  the 
surplus  hydrogen  above  that  necessary  to  form  water  with  the 
oxygen  which  need  be  considered;  or  instead  of  using  the  total 
per  cent  or  weight  of  hydrogen,  the  latter  is  diminished  by  one- 
eighth  of  the  weight  of  oxygen,  since  one  part  of  hydrogen  by 
weight  goes  to  eight  weights  of  oxygen. 

Suppose,  for  example,  in  the  case  of  a  gas,  its  analysis  gives 

H 22.    percent 

CH4 67.      ."     " 

CTT  _,  it  ft 

2^4 5  ' 

C3H8 i.  "  " 

CO 0.6  "  " 

C02 0.6  "  " 

N 3-0  "  " 

O  .  0.8  "  " 


100. 0 

Then  the  volume  of  air  for  its  combustion  per  cubic  foot  will 
be  found  by  the  following  calculation: 

H     will  require  .22X2.38  =0.52360  cu.  ft. 

CH4    "        "       .67X9.52  =6.37840  "     " 

C2H4  "        "       .o5X(2  +  f)X4.75  =0.71250  "    " 

C3H8"        "       .oiX(3+f)X4.75  =0.23750"    " 

CO    "        "       .006X2.38  =0.01428  "    " 


Total  air  for  imflammable  gases  =  7 . 86628  " 
Subtract  for  oxygen  .  008  X  4 . 7  5  =    .  03800  " 

Total  air  for  mixture 7 .82828  " 


28  THE  GAS-ENGINE, 

If,  instead  of  a  gas;  the  fuel  analyzed  were  a  liquid,  the  table 
in  the  preceding  paragraph  enables  the  computation  to  be  easily 
made  from  a  formula  in  the  form 


C  \  H 

Vol.  of  air=(i4oX— 1  +  421— > 


I.  of  air=( 

which  can  be  written  without  sensible  error 
F=i.4o(C+3H 

if  the  computations  be  made  for  32°  F.  and  the  fuel  has  no  oxygen. 

For  example,  let  an  oil  be  chosen  with  an  analysis 

Carbon  ......................  .....  .........  84 

Hydrogen  ..................................  16 

i  oo 

Then  the  volume  of  air  in  cubic  feet  at  32°  will  be 

7=1.40  (C+3H)  =  1.40(84+  48)  =  184.8. 

At  62°  it  will  be  about  200  cubic  feet.     If  the  fuel  contain  oxygen 
and  sulphur,  then  as  before 

Each  per  cent  of  C  requires  i4oX  C-MOO  cu.  ft.  of  air, 
"      "      "     "   H       "        24IXH-MOO     "       "   " 

"         "         "        "     S  "  52XS-MOO        "          "     " 

so  that  the  above  principle  gives 


Volume  of  air  = 


100 


By  weight,  for  a  fuel  containing  C  and  H, 

Weight  of  air=ii.3C+34(H--g-j 

This  is  more  usually  written: 

/        O\ 

Weight  of  air  =120+36  (H--g-K 


LIBERATION  OF  HEAT  ENERGY.  29 

It  will  be  found  convenient  to  establish  a  relation  between 
the  weight  of  the  combustible  and  the  weight  of  the  fuel  and  air 
required  for  its  complete  combustion.  If  the  weight  of  the  fuel 
be  called  y  and  the  weight  of  air  for  its  combustion  be  called  x, 
then  the  ratio  between  weight  of  fuel  and  weight  of  its  products 
of  combustion,  which  may  be  called  Krt  will  be  denoted  by 


and  may  be  called  its  "combustion  ratio." 

For  carbon,        Kr  =  -  -=  .  0813 
"    hydrogen,     Kr=  —      =  .0285 

OJ 

"    marsh-gas,  Kr=-^      =.0555 
"    ethylene,      Kr=  —  7-  =  .0461 

The  use  of  this  ratio  of  combustion  will  appear  when  computa- 
tions are  desired  as  to  the  increase  in  temperature  due  to  com- 
bustion, and  the  quantity  of  fuel  is  given  in  pounds  instead  of 
cubic  feet  as  in  the  calculations  based  on  the  data  in  parag.  29. 
While  the  computations  by  weight  made  hitherto  are  general 
by  reason  of  their  independence  of  temperature,  yet  since  in  gas- 
engine  problems  the  resulting  volume  from  a  combustion  is  often 
of  prime  consequence,  attention  must  be  directed  to  certain 
phenomena  peculiar  to  this  action.  The  law  of  Avogadro,  that 
under  the  same  conditions  of  pressure  and  temperature  equal  vol- 
umes of  all  gaseous  substances  whether  elementary  or  compound 
contain  the  same  number  of  molecules,  makes  it  apparent  that 
when  a  new  substance  is  formed  by  a  chemical  union  of  atoms 
(J  of  the  molecule)  it  does  not  follow  that  the  new  volume  is  the 


THE  GAS-ENGINE. 


sum  of  the  elemental  volumes.  On  the  contrary,  this  relation  is  the 
exception,  and  experiment  shows  that  the  volume  of  a  compound 
gas  made  up  of  elements  which  combine  in  relations  of  i :  i  are 
the  only  ones  which  make  the  compound  gas  twice  that  of  the 
elemental  ones.  For  example,  when  two  volumes  of  hydro- 
gen (H2)  unite  with  one  volume  of  oxygen  (Oj)  to  form  water- 
vapor,  the  volume  of  the  latter  is  twice  that  of  the  oxygen,  and 
not  three  times  that  of  the  unit.  When  CO  burns  to  CO2  one 
additional  volume  of  oxygen  is  required,  but  the  resulting  gas 
occupies  only  two  volumes.  In  the  case  of  marsh-gas  (CH4) ,  the 
C  requires  two  volumes  of  O,  which  will  occupy  two  volumes, 
and  the  H4  will  also  require  two  volumes  O,  which  will  occupy 
twice  two  or  four  volumes,  making  6  in  all.  Hence  since  CH4, 
being  a  compound,  occupies  2  volumes,  to  secure  complete  com- 
bustion of  both  elements  there  must  be  added  4  volumes  of  oxygen 
to  2  volumes  of  CH4,  making  also  6,  and  there  is  neither  increase 
nor  decrease.* 

If  several  of  these  computations  be  tabulated,  the  following 
figures  result: 

TABLE. 


Line 

No. 

Result  for  i  cu.  ft.  of 

H 

CH4 

Q>H4 

CO 

C4Hs 

j 

Oxygen  required  in  cu.  ft.       .    ..... 

O.  C.O 

2    OO 

3.    OO 

o  qo 

6  oo 

2 

•2 

Volume  of  N  in    air  to  supply  O, 
4-75—  1.00=  3-75X  vol.  of  oxygen.  . 
Volume  of  air  —  sum  of  i-|-2.    ..    ... 

1.87 

2.77 

7-50 
Q.  Co 

11.25 
14-  2C 

1.87 

2.  77 

22.50 
28.  qo 

4 

Total  volume  when  oxygen  is  used, 
line  i  -\-  unit  weight.                     .... 

I  .  ^O 

7.OO 

4-OO 

I  .  ^O 

7.00 

5 

Total  volume  when  air  is  used,  line 
2  -|-  line  4                             

•2.  77 

IO.  <O 

1^-2^ 

7.  7,7 

2Q.  CO 

6 

Volume  after  combustion  when  oxy- 

I.OO 

7 

4 

I 

8 

7 

Volume  after  combustion  when  air  is 
used,  line  6  +  line  2  

2.87 

10.50 

15.25 

2.87 

7O.qO 

8 

Change  of  volume  when  O  is  used, 
line  6  —  line  4                        

—  .SO 

0 

O 

—  .50 

+  1 

9 

Change  of  volume  when  air  is  used, 
line  7  —  line  5                      

—  .50 

O 

0 

—  ."JO 

+  1 

15.  Calorific   Power   of   a  Fuel.— The    calorific   power  of  a 
fuel  is  the  amount  of  heat  expressed  in  thermal  units  (par.  39) 

*  See  also  the  tabular  data  in  the  taMe  of  elementary  gases,  pat-ag.  29. 


LIBERATION  OF  HEAT  ENERGY.  31 

which  is  liberated  upon  the  combustion  of  a  unit  of  weight  of 
the  combustible  material.  The  calorific  power  of  a  fuel  does 
not  depend  upon  the  rapidity  of  the  combustion,  nor  on  the  time 
taken  in  the  process  of  absorbing  the  total  heat  resulting  from  it. 
The  temperature  produced  by  the  combustion  does  depend 
upon  the  rate  at  which  the  combustion  takes  place.  Values  for 
various  calorific  powers  of  different  fuels  are  given  in  the  follow- 
ing tables  in  connection  with  the  discussion  of  such  fuels.  It 
should  be  noted  that  the  calorific  power  as  determined  by  most 
of  the  calorimeters  gives  a  figure  not  directly  applicable  to  gas- 
engine  calculations,  since  the  gases  are  discharged  cold  from  the 
measuring  apparatus,  with  the  products  of  combustion  con- 
densed by  the  absorbing  medium,  so  that  the  latent  heat  of  their 
condensation  is  credited  to  the  calorific  power  of  the  gas.  In  the 
internal-combustion  engine,  on  the  other  hand,  the  heat  is  gen- 
erated in  the  presence  of  hot  gases  which  are  not  condensed  in 
the  apparatus  itself  but  escape  as  vapors.  When  all  the  water 
produced  by  the  combustion  and  the  steam  thus  formed  is  con- 
densed, the  result  of  the  computation  is  called  the  "higher 
heating  or  calorific  value."'  In  the  computation  of  the  "lower 
calorific  value"  the  steam  formed  is  assumed  to  be  present  as 
dry  saturated  steam,  having  965  units  of  heat  latent  from  32°, 
or  a  total  expenditure  from  64°  to  212°  of  116  in  the  liquid  and 
965  in  the  gas,  making  1081  in  all.  The  lower  value  will  differ 
from  the  higher  by  deducting  this  quantity  of  heat  from  the 
higher  for  every  pound  of  water  produced  by  the  combustion 
cf  one  pound  of  gas.*  In  France  the  higher  heating  value  is 

*  As  examples  of  the  method  to  be  followed  in  computing  the  difference  between 
the  high  and  low  values  the  following  may  be  used  as  guides: 

With  methane,  CH4  the  atomic  weight  of  the  fuel  is  16. 

The  atomic  weight  of  resulting  CO2  and  H2O  is  ...  80. 

The  water  is  36  parts  of  this  80,  or  is  2%  by  weight. 

If  the  fuel  weighs  16  and  the  products  weigh  80,  the  fuel  is  |f  of  such  pro- 
ducts, or  if  the  fuel  weighed  i  pound  the  products  would  weigh  5. 

Hence  the  water  is  ^j  of  5  pounds,  or  2\  pounds. 

2\  pounds  withdraw  1080  heat  units  per  pound  in  cooling  from  steam  at  212° 
to  water  at  64°,  or  2428  heat  units  in  all. 


32  THE  GAS-ENGINE. 

preferred,  and  is  used  by  Witz  and  others,  on  the  ground  that  it 
is  a  defect  in  the  gas-engine  that  it  should  not  utilize  this  latent 
heat  as  the  steam-engine  can,  to  produce  external  work,  and  the 
gas  computation  should  be  made  in  fairness  to  the  gas  on  the 
basis  of  the  possession  of  this  ability.  In  America,  Germany, 
and  England  the  lower  value  is  used  because  the  steam  cannot 
be  condensed  in  practice,  and  heat  being  latent  and  remaining 
so,  it  does  not  communicate  anything  to  the  effective  cycle. 
Experiments  should  always  report  which  value  of  the  heating 
power  of  the  gas  is  used,  since  the  difference  will  rarely  be  less 
than  five  per  cent  in  actual  examples,  and  may  reach  ten  per  cent. 
The  following  table  [from  Geitel*]  shows  three  typical  gas  values, 
in  meters  and  feet  and  in  kilograms  and  pounds : 

With  ethylene  C2H4  the  atomic  weight  of  the  fuel  is  28. 

The  atomic  weight  of  resulting  products  of  combustion  is  124. 

The  water  is  36  parts  of  this  weight,  or  approximately  £ 

If  the  fuel  weighs  28  and  the  products  of  combustion  124,  one  pound  of  fuel 
makes  4.4  pounds  of  products  of  which  f  is  water,  ij  pounds  of  products  is  water. 
Hence  these  withdraw  1080  per  pound  or  1388  in  all. 

With  benzene  CCH6  the  fuel  weighs  72,  the  products  183.  The  water  is  54  of 
this  or  practically  £. 

One  pound  of  fuel  makes  a  little  over  four  pounds  of  products.  Hence  the 
Tveight  of  water  in  the  products  is  f  of  a  pound  so  that  $  of  1080  or  720  units  are 
withdrawn. 

With  butylene  C4H8  the  fuel  weighs  56  and  the  products  248  so  that  one  pound 

of  fuel  makes  ~  =  4.4  pounds  of  products.     Of  these  the  H2O  is  -*-=  =  £   prac- 
50  240 

tically  or  the  water  is——  =  1.4  pounds.  Hence  1.4  X  1080  =  1512  heat  units 
withdrawn. 

*  Das  Wassergas  und  seine  Verwendung  in  der  Tecknik.  To  transform  calo- 
ries per  cubic  meter  into  B.T.U.  per  cubic  foot  the  factor  to  be  used  in  multiplying 
the  former  approximates  8.91.  An  average  of  9  in  round  figures  will  give  con- 
cordant results. 


LIBERATION  OF  HEAT  ENERGY. 


33 


HEATING   VALUES    HIGH    AND    LOW    FOR   THREE   KINDS 

OF   GAS. 


Unit  Used. 

Calories  per 
Cubic  Meter. 

B.T.U.  per 
Cubic  Meter. 

Calories  per 
Kilogram. 

B.'l  .U. 
per  Pound. 

Water    of     Com- 
bustion as      .    . 

Liquid 

Gas 

Liquid 

Gas 

Liquid 

Gas 

Liquid 

Gas 

Calorific  Value    . 

High. 

Low. 

High. 

Low. 

High. 

Low. 

High. 

Low. 

Lighting  Gas 
Power  Gas  .   . 
Water  Gas  .    . 

5810 
1048 
3°54 

5154 
1048 
2813 

650 
117 
332 

577 
117 

3i5 

ii>35° 

838 
4,558 

10,070 
838 
4,199 

20,430 
1,508 
8,204 

18,126 
1,508 

7,558 

1 6.  Fuel  Calorimeters.  Mahler  Bomb. — The  calorific  power 
of  a  fuel  is  a  matter  of  experimental  observation.  The  general 
method  used  in  determinations  is  to  cause  a  known  weight  of  the 
fuel  to  burn  in  a  closed  vessel  into  which  oxygen  is  introduced 
and  the  fuel  ignited  in  the  atmosphere  of  oxygen.  The  closed 
vessel  is  surrounded  by  an  observed  weight  of  water  at  an  observed 
temperature,  which  is  usually  made  to  circulate  so  as  to  maintain 
a  constant  temperature  in  order  that  no  variation  in  the  value  of 
the  specific  heat  may  occur.  The  number  of  heat-units  absorbed 
by  the  rise  of  that  weight  of  water  through  its  observed  range  of 
temperature  gives  the  calorific  power  of  the  fuel  tested,  so  that  the 
apparatus  is  correctly  called  a  calorimeter  or  measurer  of  heat. 

One  of  the  best  known  of  the  calorimeters  is  that  of  Mahler, 
sometimes  called  the  Mahler  Bomb.  In  a  very  usual  form  of 
this  apparatus,  shown  in  Fig.  i,  B  is  a  thick  steel  chamber  lined 
with  porcelain  in  order  to  prevent  any  chemical  action  between 
the  steel  of  the  vessel  and  the  fuel  burned  within  it.  A  weighed 
amount  of  the  fuel,  whether  as  a  solid  pulverized,  or  as  a  liquid  in 
the  form  of  an  oil,  is  introduced  into  a  platinum  pan,  C,  into  the 
bomb,  and  then  a  large  excess  of  oxygen  gas  at  a  pressure  of  300 
pounds  per  square  inch,  or  thereabout,  is  introduced  to  surround 
the  pan.  An  electric  circuit  is  completed  through  a  wire  of 
small  cross-section  where  it  touches  the  fuel,  so  that  it  shall  be- 
come red-hot  when  the  current  meets  the  resistance  of  that  small 
section.  This  brings  the  combustible  to  the  firing-point,  so  that 
in  the  dense  atmosphere  of  oxygen  it  burns  completely.  The 


34 


THE  GAS-ENGINE. 


water,  D,  which  surrounds  the  bomb  in  an  outer  vessel  is  agitated  by 
a  stirring  apparatus,  S,  in  order  to  keep  its  temperature  uniform 
throughout.  Carefully  calibrated  thermometers  of  high  accuracy, 
reading  to  the  hundredth  of  one  degree,  record  the  temperature 
rise  in  the  enveloping  water,  A,  and  the  outer  jacket  is  heavily 
felted  so  as  to  prevent  loss  of  heat  by  radiation  to  the  surround- 


FIG.  i. 


ing  air.  The  rise  in  the  temperature  of  the  water  is  less  than 
that  due  to  the  combustion  of  the  fuel  by  the  absorption  of  heat 
by  the  metal  of  the  bomb  itself  in  reaching  the  temperature  of  the 
combustible  within  it.  This  is  determined,  experimentally,  by 
calibration  and  is  usually  called  the  constant  of  the  calorimeter. 
It  can  conveniently  be  expressed  as  a  quantity  of  water  which 
would  absorb  the  same  quantity  of  heat  for  each  single  degree 
increase  of  temperature  as  the  metallic  parts  of  the  calorimeter 
have  been  observed  to  absorb.  The  Mahler  Bomb  is  more  con- 
veniently applied  to  measurements  of  the  calorific  power  of  solid 
and  liquid  fuels  than  of  gases. 


LIBERATION  OF  HEAT  ENERGY. 


35 


17.  The  Junker  Gas  Calorimeter.— The  Junker  gas  calorim- 
eter has,  as  one  of  its  advantages,  the  fact  that  readings  can  be 


FIG.  2. 


taken  continuously  with  it  over  a  considerable  period  of  time,  so 
that  the  percentage  of  errors  due  to  observation  becomes  less, 
and  also  variations  in  the  quality  of  the  gas-supply  can  be  de- 
tected, while  any  test  is  in  progress.  As  ordinarily  used,  the 
apparatus  for  the  Junker  calorimeter  is  represented  in  Fig.  2. 
The  gas  to  be  measured  is  passed  through  the  test  meter  at  the 
left  hand  of  the  cut,  which  should  be  finely  graduated  so  as  to 
read  down  to  thousandths  of  a  cubic  foot.  Next  to  this  is  a 


36  THE  GAS-ENGINE. 

pressure- regulator  so  that  all  observations  may  be  made  without 
effect  from  pulsations  in  the  gas-main  or  caused  by  the  engine  itself 
which  is  under  test.  This  pressure-regulator  is  of  the  ordinary 
construction  of  a  gas-holder.  The  tube  on  the  outside  of  the 
regulator  measures  the  pressure  by  which  the  inverted  cylindrical 
vessel  is  raised  in  the  water-seal  which  closes  the  open  bottom 
of  the  inverted  vessel.  The  reading  in  pressures  is,  of  course, 
in  inches  of  water-pressure.  From  the  pressure-regulator  the 
gas  is  led  to  the  burner  proper  which  is  introduced  into  the  bottom 
of  the  apparatus  which  forms  the  calorimeter  itself.  The  neces- 
sary quantity  of  air  for  combustion  to  produce  a  Bunsen  effect 
enters  with  the  gas  through  regulated  openings,  and  the  additional 
air-supply  comes  in  through  the  open  bottom  of  the  central  tube 
of  the  calorimeter.  The  section  of  the  calorimeter  in  Fig.  3 
shows  the  gas-flame  in  position  and  the  arrangement  whereby 
the  hot  products  of  combustion  ascend  to  the  top  into  the  space 
marked  29  and  there  descend  around  the  central  tube  and  pass 
out  at  the  bottom  through  the  tube  32  in  small  tubes  which  are 
completely  surrounded  by  the  enveloping  cooling  water.  This 
cooling  water  is  supplied  to  an  overhead  vessel  through  the  pipe  i. 
The  chamber  3  is  open  at  the  top  so  that  any  excess  of  supply 
beyond  what  passes  through  the  calorimeter  is  discharged  through 
the  tube  5.  A  constant  head  for  the  flow  is  thus  maintained 
in  spite  of  variations  in  the  supply.  The  cold  water  enters  at 
the  bottom  and  is  discharged  at  the  top  by  overflowing  in  a 
funnel  20.  A  thermometer,  12,  in  the  inlet  and  a  thermometer, 
43,  in  the  outlet  measure  the  range  of  temperature  caused  by 
the  combustion.  The  rapidity  of  the  flow  of  the  water  is  con- 
trolled by  the  plug-cock  9,  with  a  view  of  having  the  rise  in  tem- 
perature kept  within  convenient  limits.  The  outlet  35  from  the 
bottom  of  the  hot  chamber  is  intended  to  remove  any  condensed 
water  which  may  result  from  the  combustion  of  hydrogen.  The 
whole  cylinder  and  top  of  the  calorimeter  are  surrounded  with 
an  air-jacket  to  prevent  radiation  from  the  water  used  in  absorbing 


LIBERATION  OF  HEAT  ENERGY. 


37 


the  heat  of  the  gases.     The  use  of  the  apparatus  will  be  plainly 
evident  from  the  illustration.     When  the  pointer  of  the  meter 


GAS  8UPPQ1 


FIG.  3. 

passes  the  zero  mark  the  discharge  from  the  overflow  C  is  trans- 
ferred from  the  waste  to  the  graduated  vessel,  and  the  tempera- 


38  THE  GAS-ENGINE. 

lure  of  the  hot-water  thermometer  is  observed  at  intervals  while 
the  glass  is  filling.  The  cold-water  thermometer  is  not  likely 
to  change  its  reading.  When  the  measuring-glass  is  filled  to  a 
designated  point  the  meter  reading  is  taken  to  determine  the 
cubic  feet  of  gas  burned,  and  its  heating  value  is  computed  by 
the  following  simple  formula: 

HG  =  WT, 

in  which  H  is  the  calorific  value  of  one  cubic  foot  of  gas  and  G 
the  quantity  of  cubic  feet,  by  meter,  burned  during  the  experiment. 
Then  if  W  is  the  weight  of  water  passed  through  the  apparatus 
while  the  volume  of  gas  was  burning,  and  T  is  the  difference 
between  the  thermometer  readings  at  the  inlet  and  outlet  ends 
of  the  apparatus,  the  equation  can  be  solved  for  each  directly. 
As  the  apparatus  is  continuous  it  does  not  need  a  correction  for 
the  calorimetric  constant,  since  after  the  apparatus  has  once 
been  heated  this  quantity  is  the  same  at  the  beginning  and  end 
of  the  experiment.  Obviously,  if  the  gas  containing  hydrogen 
deposits  a  certain  amount  of  water  in  the  annular  space  31,  the 
value  given  by  the  above  formula  will  be  a  gross  value,  since  the 
water  formed  by  the  combustion  of  the  hydrogen  will  have  given 
up  its  latent  heat  to  the  circulating  water.  Junker's  calorimeter 
is  usually  constructed  so  that  the  measuring-glass  reads  in  litres, 
making  one  litre  weigh  a  kilogram.  The  result  will  therefore 
be  given  in  this  form  of  the  apparatus  in  calories,  which  can  be 
transformed  to  British  thermal  units  by  multiplying  by  the  factor 
3.9683,  which  is  usually  called  4.  Since  the  combustion  in  the 
calorimeter  chamber  takes  place  at  atmospheric  pressure,  the  con- 
densation of  one  pound  of  the  watery  vapor  will  set  free  966  B.T.U. 
The  weight  of  condensed  water-vapor  in  pounds  multiplied  by 
966  plus  the  range  above  32°  for  the  condensing  water,  usually 
bringing  it  to  1080,  will  give  the  absorption  of  B.T.U.  for  the 
weight  of  gas  burned.  If  the  gases  were  to  be  used  hot,  this 
condensation  would  not  occur. 


LIBERATION  OF  HEAT  ENERGY. 


39 


18.  The  Lucke  Gas  Calorimeter. — A  form  of  calorimeter 
particularly  adapted  to  measure  the  heat  generated  when  ex- 
plosive mixtures  of  gas  and  air  are  ignited  and  burn  under  con- 
stant pressure  is  the  result  of  the  investigations  of  Dr.  C.  E. 
Lucke  concerning  the  conditions  suitable  and  necessary  for  the 
combustion  of  such  mixtures  under  constant  pressure.  The 
apparatus  is  illustrated  in  Fig.  4.  A  suitable  vessel  to  contain 


water  surrounds  an  ordinary 
pipe 'fitting  of  the  desired  size 
F  which  is  bushed  at  the 
bottom  to  receive  a  copper 
pipe  E  for  the  delivery  of  the 
explosive  mixture.  The  mix- 
ture is  ignited  in  the  tee  by 
a  spark  plug  of  the  sort  which 
is  usual  in  gas-engine  practice, 
inserted  at  G  and  connected 
with  the  necessary  electric 
wires  for  the  passage  of  a  jump 
spark.  The  explosive  mixture 

burns  throughout  the  broken  magnesite  in  the  tee,  and  the  hot 
products  of  combustion  pass  out  through  the  connection  H  which 
leads  them  to  a  square  coil  of  pipe  whereby  their  temperature 
is  withdrawn  by  means  of  the  water  circulating  in  the  chamber. 
This  water  is  measured  as  to  weight  and  temperature  as  in  the 
previous  formula.  The  end  of  the  square  coil  can  be  connected 
by  rubber  and  glass  tubes  so  that  the  products  of  combustion  can 
be  directed  to  any  point  in  the  water-chamber  so  as  to  act  as  a 


FIG.  4. 


40  THE  G4S-ENGINE. 

stirrer.  The  glass  bottle  B  is  to  serve  as  a  trap  for  convenience 
in  the  delivery  of  the  entire  quantity  of  explosive  mixture  as  re- 
ceived from  a  measuring  apparatus  connected  to  B  by  the  tube  A . 

19.  Calorific  Power  of  a  Compound. — The  calorific  power 
of  a  compound  will  be  the  sum  of  the  calorific  powers  of  its  com- 
ponents, provided  that  in  the  chemical  reactions  of  the  combustion 
there  does  not  occur  an  absorption  of  heat  at  the  expense  of 
their  surroundings.  When  heat  is  liberated  as  the  outcome  of 
the  chemical  change,  the  reaction  is  called  exothermic;  when 
heat  is  absorbed  by  the  reaction  it  will  be  called  an  endothermic 
reaction.  The  discussion  which  follows  is  made  on  the  assump- 
tion for  simplicity  that  the  compound  has  the  exothermic  property. 

The  proportions  of  the  components  may  either  be  the  result 
of  the  known  chemical  combination  for  a  true  chemical  com- 
pound, or  may  result  from  a  chemical  analysis  which  shall  deter- 
mine the  percentage  of  the  elements  in  the  compound.  For 
example:  if  the  gas  is  a  chemical  compound  such  as  olefiant  gas, 
C2H4,  which  is  made  up  of 

C2  +  H4  =  24  +  4  =  28  parts  by  weight, 

A  =  T  wiU  be  hydrogen,  and  ffc  =  f  will  be  carbon.  If,  then, 
Y  of  the  calorific  power  of  hydrogen  be  added  to  f  of  the  calorific 
power  of  carbon,  their  sum  will  be  the  calorific  power  of  the 
compound.  With  analyzed  hydrocarbons  the  percentage  of  each 
constituent  will  be  used  instead  of  the  fraction  above. 

The  accepted  *  formula  for  computing  the  calorific  power 
from  a  fuel  analysis  is  due  to  the  physicist  Dulong  and  is  known 
by  his  name.  It  has  the  form 

Calorific  power  of  i  Ib.  in  B. T.U.  =  14,6000+62, ooo/H-  — 

\         o 

In  this,  C,  H,  and  O  are  the  percentages  respectively  of  car- 
bon, hydrogen,  and  oxygen,  divided  by  100  to  reduce  them  to 
actual  fractions  of  one  pound.  This  is  often  transformed  by 

*  The  Dulong  formula  is  accepted  as  correct  within  limits  of  error  of  5  per  cent, 
the  accuracy  or  error  varying  with  the  composition  of  the  coal. 


LIBERATION  OF  HEAT  ENERGY.  41 

the  expedient  of  factor'ng  the  constants  denoting  the  respective 
calorific  powers  of  carbon  and  hydrogen  so  as  to  read 

Calorific  power  =14,600   0+4.25(1!——)    , 


snce 

If  desired  to  take  account  of  the  sulphur  present  by  analysis, 
or  to  express  the  formula  in  centigrade  and  metric  units,  the 
equation  takes  the  two  forms: 

Heating  value  in  B.  T.  U.  =  T^[i  4,6000+62,  ooo  (H  —  —j  +40508]. 
Heating  value  in  calories  =y  ^[8  1  400  +  34,  400  (H—  —  j  +22508]. 

Mahler's  equation  in  parallel  form  is: 

Heating  value,  calories=  y$v[8i4oC  +  34,5ooH  —  3000(0  +N)]. 
In    the    above   C  =  Carbon,  H  —  Hydrogen,  O  =  Oxygen,  N  =  Nitrogen, 
S  =  Sulphur. 

20.  Computed  Increase  in  Temperature  Due  to  a  Com- 
bustion. —  It  will  appear  in  a  later  paragraph  'par.  54)  that  each 
body  requires  a  certain  amount  of  heat  to  raise  the  temperature  of 
one  unit  weight  of  that  material  by  one  degree  on  the  thermometric 
scale.  This  quantity  of  heat,  called  its  specific  heat,  seems  to 
bear  a  constant  ratio  to  its  atomic  weight  (specific  heat  X  atomic 
weight  =  6.  25  approx.)  and  is  usually  designated  by  the  initial  C. 
Hence,  if  one  pound  of  air  be  raised  from  7\  to  T2,  the  heat  -units 
H  to  do  this  will  have  to  be  H  =  C(T2-T1). 

If  the  calorific  power  of  one  pound  of  a  fuel  be  denoted  by  Q 
in  British  thermal  units,  and  y  denote  the  weight  in  pounds,  and 
x  the  weight  of  air  to  burn  it  (paragraphs  11-13),  then  x+y 
will  be  the  weight  of  gases  present,  and  (x+y)C  will  be  the  amount 
of  heat  required  to  raise  this  mixture  one  degree.  But  the  total 
heat  corresponding  to  H  above  will  be  yQ.  Hence  for  x+y 
pounds 

yQ  =  (oc+y)C(T2-T1), 


4  2  THE  GAS-ENGINE. 

or 


From  this  if  Q  be  known  from  experiments  in  calorimetry, 

/y 

and  the  combustion  ratio  -~  =Kr  be  computed  and  C  be  given 

from  the  work  of  the  physicist,  the  rise  in  temperature  can  be 
calculated.  This  is  the  theoretical  temperature  of  combustion 
on  the  assumption  that  the  actual  specific  heat  is  known  and  does 
not  change  during  the  process. 

If  the  calorific  power  of  carbon  be  called  14,000,  and  the  ratio 

y       j 

•    .     =  -—  =  .0813,  and  C  have  an  average  value  of  .237,  then 

:.!;•.   ^-^=.08x3x^=4800°    I 

when  the  heating  is  done  under  the  condition  of  constant  pressure, 
and  the  effective  specific  heat  be  called  that  of  air  under  these 
conditions.  If  the  figure  .169  be  used,  as  determined  by  Reg- 
nault  for  air  at  constant  volume,  then 


It  will  appear  in  the  later  discussion  that  no  such  tempera- 
tures are  realized  in  actual  practice  with  engines  and  combustion 
in  the  cylinders,  even  when  fuels  rich  in  hydrogen  are  used,  with 
higher  calorific  powers.  Hence  it  becomes  significant  to  ascer- 
tain what  the  value  of  the  actual  or  effective  specific  heats  of  the 
gaseous  mixtures  are,  and  whether  these  are  constant  for  all 
temperatures.  A  full  discussion  of  this  question  will  appear 
in  par.  55.  It  becomes  important  to  ascertain  what  effect  the 
cooler  metals  of  the  piston  and  cylinder  walls  have  in  dissipating 
the  heat  due  to  combustion,  and  whether  any  other  phenomena 
appear  of  chemical  character  which  will  account  for  this  suppres- 


LIBERATION  OF  HEAT  ENERGY.  43 

sion  of  heat.     The  actual  temperatures  are  deduced  from  maxi- 
mum observed  pressures  by  the  formula 


= 

T0      TV 

so  that 


in  which  p0TQ  are  the  pressures  and  temperatures  before  the 
combustion  occurred,  and  pt  the  observed  pressure  resulting 
from  the  combustion;  but  these  computations  give  values  much 
below  the  values  computed  by  the  foregoing  method. 

21.  Dissociation. — Doubtless  one  cause  for  the   lowering  of 
the  actual  temperature  of  combustion  below  the  computed  theo- 
retical value  in  an  engine  cylinder  is  a  decomposition  of  chemical 
combinations  by  reason  of  the  high  temperature.     Such  a  breaking 
up  of  gaseous  compounds  is  called  "the  dissociation  of  gases," 
and  absorbs  as  much  heat  as  the  formation  of  such  combinations 
would  liberate.     Water-vapor,  for  instance,  which  is  a  product 
of  the  combustion  of  hydrogen,  is  broken  up  at  between  1600° 
and  1800°  Fahr.  into  component  H  and  O;  and  while  the  hydro- 
gen will  recombine  on  a  reduction  of  temperature  during  expan- 
sion, it  may  occur  late  enough  to  be  incomplete  before  the  exhaust 
opens.     Or,  the  lowering  of  temperature  by  the  cooled  cylinder- 
walls  may  prevent  complete  recombination. 

22.  Sources  of  Gaseous  Fuel  for  Gas-engines. — The  hydro- 
carbon or  carbon  gases  which  are  used  in  gas-engines  are  of  three 
kinds.     The   first   is   natural   gas,    received   from    subterranean 
sources  as  the  result  either  of  distillation  now  in  progress  under- 
ground, or  the  accumulations  of  previous  distillations  which  have 
ceased.     The    second    would    be    designated    as    producer-gas, 
which  is  a  manufactured  article  made  by  the  distillation  of  solid 
fuel  by  heat.     This  gas  is  of  two  kinds.     The  first  would  be 
designated  as  fuel-gas  and  is  a  product  rich  in  carbon  but  poor 


44  THE   GAS-ENGINE. 

in  hydrogen.  The  second  group  is  the  kind  of  gas  which  is 
made  for  illuminating  purposes  and  is  distributed  through  the 
mains  of  the  cities.  It  is  richer  in  illuminants  than  the  true 
producer-gas,  but  producer-gas  can  be  enriched  so  as  to  be  made 
into  illuminating-gas.  Belonging  to  this  producer  group  is  the 
outflow  of  gas  from  the  top  of  the  blast-furnace  used  in  the  smelt- 
ing of  iron  from  its  ores.  This  is  a  gas  usually  leaner  than  the 
other  two  in  calorific  power,  containing  little  or  no  hydrogen. 
It  carries  with  it  a  considerable  quantity  of  finely  divided  dust 
from  the  limestone  or  other  material  in  the  furnace,  whose  re- 
moval must  be  provided  for  in  the  design  of  the  engine  which 
uses  this  gas.  The  third  kind  of  gas  is  really  a  carburetted  air, 
made  by  saturating  atmospheric  air  with  the  volatile  constituents 
of  a  liquid  hydrocarbon,  as  discussed  in  Chapter  X. 

Where  oil  is  the  source  of  heat  energy,  it  will  be  made  into  a 
gas  and  will  be  thus  used  in  the  motor.  It  may  be  made  into  a 
gas  by  a  distilling  process  whereby  the  liquid  oil  is  injected  into 
a  hot  chamber  or  into  a  chamber  so  filled  with  heated  air  that  the 
liquid  becomes  a  vapor  by  the  process  of  vaporization,  which 
is  analogous  to  a  distillation  by  heat.  Or  a  more  volatile  hydro- 
carbon liquid  may  be  used  and  the  air  which  is  to  serve  as  a 
medium  and  is  to  support  the  combustion  of  the  hydrocarbon 
may  be  sent  through  thin  layers  of  the  hydrocarbon  so  that 
the  air  will  pick  up  and  carry  with  it  a  mist  or  vapor  of  the 
volatile  hydrocarbon.  This  makes  a  species  of  air-gas  having 
the  properties  of  the  foregoing  with  respect  to  ignition  and  other 
behavior,  and  is  a  form  of  gas  much  used  in  motors  for  automobile 
practice. 

23.  Natural  Gas. — In  certain  parts  of  the  United  States  of 
America,  notably  in  Pennsylvania,  Ohio,  and  Indiana,  large 
accumulations  of  a  natural  fuel-gas  are  found  in  subterranean 
cavities  or  strata  which  can  be  reached  by  wells  drilled  from  the 
surface  of  the  ground.  Such  gas  is  usually  under  considerable 
pressure,  so  that  it  can  be  piped  from  its  sources  to  industrial  cen- 
tres without  too  great  loss  of  pressure,  or  artificial  pressure  may 


LIBERATION  OF  HEAT  ENERGY. 


45 


be  secured  by  proper  gas-pumps,  which  may  themselves  be  con- 
veniently operated  as  gas-engines. 

The  varying  districts  give  varying  constitutions  of  the  gas 
and  hence  a  calorific  power  which  varies.  In  the  neighborhood 
of  Pittsburg,  Pa.,  one  pound  of  coal  is  considered  to  be  equivalent 
to  yj  to  12 J  cubic  feet  of  gas.  The  following  tables  give  some 
analyses : 

VARIATION  IN  COMPOSITION  OF  NATURAL  GAS. 


Constituents. 

i 

2 

3 

4 

5 

6 

Marsh-gas  

^7-^8 

7^  .16 

72.l8 

6$.2Z 

60    7O 

40    ^8 

Hydrogen  

O.6A 

14.4^ 

2O.O2 

26.16 

2Q    Ot 

3^  02 

Ethylic  hvdride  

EC.2O 

4.80 

V6o 

^.^o 

7    02 

12     ^O 

Olefiant  gas  

0.80 

0.60 

0.70 

0.80 

/  -v-6 
o  08 

I 

o  60 

Oxygen 

2.IO 

i.  20 

I.IO 

0.80 

o  78 

o  80 

Carbonic  oxide  

I.OO 

o.  to 

i  .00 

0.80 

*  / 

o  c8 

o  40 

Carbonic  acid   

O.OO 

O.  T.O 

0.80 

0.60 

o  oo 

o  40 

Nitrogen  

2^-41 

2.80 

O.OO 

O.OO 

o  oo 

o  oo 

Analyses  from  various  wells  in  Indiana  and  Ohio  are  given 
in  the  table  in  parag.  29. 

24.  Producer-gas. — Gas  made  by  distilling  and  volatilizing 
the  separable  elements  in  bituminous  or  anthracite  coal  in  a 
closed  furnace,  using  part  of  its  own  heat  of  combustion  to  effect 
the  chemical  reactions,  is  often  called  producer-gas,  from  the 
name  given  to  the  gas-generator.  A  thick  bed  of  fuel 
rests  upon  properly  constructed  grates,  and  air  or  steam 
or  both  are  forced  from  below  the  grates  up  through  the  bed 
of  fuel.  The  first  combustion  is  to  carbonic  acid  (CO2)  with  air 
alone,  or  to  CO2  and  hydrogen  if  steam  is  used  also.  This 
carbonic  acid  gas,  meeting  the  layers  of  carbon  above  where  no 
free  oxygen  reaches,  is  decomposed  by  the  carbon  into  two  units  of 
carbonic  oxide  (CO),  which  with  the  hydrogen  passes  up  through 
the  bed  of  fuel  and  outwards  through  a  proper  pipe  to  the  place 
where  it  may  meet  the  required  oxygen  and  be  burned  at  the 
point  desired.  Early  producers  of  the  Siemens  type,  operating 
with  open  ash-pits  and  no  pressure  below  the  grates,  lost  much 


46 


THE  GAS-ENGINE. 


of  their  possible  effectiveness  in  the  cooling  of  the  gases  after 
leaving  the  producer.  This  loss  is  estimated  at  30  per  cent. 
To  blow  with  air  alone  is  to  introduce  inert  nitrogen  which  dilutes 
the  gas  and  lowers  its  calorific  power.  On  account  of  the  loss 
of  heat  in  the  producer  itself  in  the  distilling  process,  and  some 
loss  in  the  dissociation  of  the  water,  which  is  not  all  recovered, 
producer- gas  usually  carries  only  87  per  cent  of  the  calorific 
energy  of  the  carbon.  Some  loss  in  unreduced  CO2  must  be 
allowed  for,  and  the  cost  of  making  the  steam  used.  82  per  cent 
is  a  more  usual  figure  when  anthracite  is  used  as  fuel  instead  of 
bituminous  coal.  Much  inferior  grades  of  fuel  can  be  used  in 
the  producer  than  could  be  used  direct,  however. 

If  an  analysis  of  85  per  cent  of  solid  carbon  be  assumed  for 
an  anthracite  stock,  with  5  per  cent  of  volatile  hydrocarbons  and 
10  per  cent  of  ash,  and  the  further  assumption  be  made  of  a  com- 
bustion of  80  pounds  to  CO  and  5  pounds  to  CO2,  the  following 
calculated  statement  of  process,  products,  and  resulting  energy 
may  be  agreed  to: 


Products. 

Process. 

Pounds. 

Cubic  Feet. 

Anal,  by 
Vol. 

80  Ibs  C  burned  to  CO  

186  66 

2C2Q    24. 

•2  •?     A 

5  Ibs.  C  burned  to  CO2  

18  33 

I  <7    64. 

2     O 

5  Ibs  vol.  HC  (distilled)  

<c  oo 

116  60 

i  6 

120  Ibs.  oxygen  are    required,    of   which    30   Ibs. 
from  H2O  liberate  H 

37^ 

712    ^O 

9        A 

QO  Ibs  from  air  are  associated  with  N   .   . 

•  to 

•2QI      O^ 

4.o6d    1  7 

<3  6 

oo-'-' 

5!4-79 

75%°-*5 

IOO.O 

For  quantitative  values,  analysis  of  the  gas  and  other  data, 
reference  should  be  made  to  the  combination  table  under 
parag.  29. 


LIBERATION  OF  HEAT  ENERGY.  47 

Energy  in  the  above  gas  obtained  from  100  pounds  anthracite: 

186.66  Ibs.  CO 807,304  heat-units 

5.00    "    CH4 117,500 

3-75    "    H 232.500 

1,157,304 

Total  energy  in  gas  per  pound 2,248 

"  "       ''  100   Ibs  of  coal — 1,349,500 

Efficiency  of  the  conversion 86  per  cent 

If  the  gas-stock  be  a  bituminous  coal  with  55  per  cent  of 
fixed  carbon,  32  per  cent  of  volatile  matter,  and  13  per  cent  of 
ash,  and  the  calorific  power  of  the  hydrocarbons  be  taken  at 
20,000  heat-units  to  the  pound,  the  table  below  results  under  the 
same  assumptions. 


Products. 


Process. 

Pounds. 

Cubic  Feet. 

Anal,  by 
Vol.  " 

50  Ibs.  C  biirned  to  CO  

116  66 

1580  7 

27   8 

S  Ibs.  C  burned  to  CO2  

i8.n 

1^7   6 

2    7 

32  Ibs.  vol.  HC  (distilled)  

32.00 

3i 

746    2 

I  •?    2 

80  Ibs.  O  are    required,   of  which    20    Ibs.,    de- 
rived from  H2O,  liberate  H  

2    cj 

47^    O 

8  -i 

60  Ibs.  O,  derived  from  air,  are  associated  with  N  .  . 

200.70 

2709.4 

47-3 

370.19 

5668.9 

99-8 

Energy  in  1 16.66  Ibs.  CO 504,554  heat-units 

1     32. oo  Ibs.  vol.  HC 640,000 

"        "       2. 50  Ibs.  H 155,000  " 

1,299,554 

Energy  in  coal 1,437,500 

Per  cent  of  energy  delivered  in  gas 90.0 

Heat-units  in  i  Ib.  of  gas 3484 

Heat -units  in  one  cubic  foot  of  gas 229.2 

Fig.  5  illustrates  the  old  type  of  Siemens  producer  without  arti- 
ficial blast,  and  Figs.  6  and  7  the  more  modern  Taylor  producer 
with  forced  steam-blast  and  revolving  grates. 


48 


THE  GAS-ENGINE. 


These  computations,  however,  make  no  allowances  for  the 
variable  losses  in  ashes,  soot,  tar,  and  pitch.  These  losses  as 
low  as  i  per  cent  in  anthracite  practice  may  rise  to  10  per  cent 


FIG   5 

%ith  bituminous  fuels.  When  the  gas  is  not  cooled,  the  tarry 
vapors  are  burned  with  the  gas;  in  gas-engine  practice,  the  tar 
must  be  removed. 

Ordinary  producer-gas  has  a  calorific  value  of  1 10  to  125  B.T.U. 
per  cubic  foot.  80  cubic  feet  of  gas  should  be  given  from  one 
pound  of  coal. 

A  bituminous  producer-gas  process  has  been  perfected  by 
.Dr.  Ludwig  Mond,  of  England,  intended  to  operate  on  slack 
and  to  recover  the  most  important  by-products  in  the  form  of 
ammonium  sulphate.  An  excess  of  steam  is  blown  into  the 
producer  with  the  air  (see  water-gas).  This  excess  increases 
the  hydrogen  component  of  the  gas,  and  the  balance  is  recovered 
later.  The  output  from  a  ton  of  slack  should  be  from  140,0x50 
to  160,000  cubic  feet  of  gas  having  a  calorific  power  of  140  to 
145  B.T.U.,  with  a  heating  value  of  from  80  to  86  per  cent  of  the 
total  energy  resident  in  the  fuel.  Under  favorable  conditions 
ammonia  will  be  recovered  equivalent  to  90  Ibs.  of  ammonium 
sulphate.  About  60  cubic  feet  of  Mond  gas  seems  to  be  required 


LIBERATION  OF  HEAT  ENERGY. 


49 


per  H.P.  in  the  gas-engine,  so  that  a  plant  large  enough  to  gasify 
one  ton  of  slack  per  hour  will  supply  from  2000  to  2500  H.P.  of 
engines,  making  the  cost  for  fuel  per  H.P.  very  low.  Otherwise 
stated,  this  gas  will  furnish  one  H.P.  per  yioihnr  of  2000  =  A  of 


FIG,  6, 


FIG.  7. 


a  pound  of  coal.  Fig.  245  shows  a  type  section  of  such  a  producer 
and  its  connections.  The  following  table  shows  an  average  analysis 
and  calorific  value  of  Mond  compared  with  illuminating  gas: 


5° 


THE  GAS-ENGINE. 


Coal  Creepe 


li 

03 
P 

02    C 

gfflfe 

Si 

* 

3 

Volume  per  cent    (gases 

saturated  at  15°  C.): 

Carbonic  oxide  (CO).. 

II.  0 

7.8 

Hydrogen  (H)    

O1"!    C 

Marsh-gas  (CH*)  

2.0 

31.8 

CTJ.H  ft-\-  benzol        .    . 

nil 

r  o 

Carbonic  acid  (CO2)  .  . 

16.5 

lii 

Nitrogen  +  moisture 

(N+HgO)  

A-i    O 

2<5 

T\?  * 

Total  volume  

IOO.O 

IOO.O 

Total  combustibles.. 

4°-5 

97-5 

Calorific  -value  (gas  dry 

at  o°  C.)  : 

In    kilogram  -  calories 

per  cubic  metre  .  . 
In  British  thermal  units 

i392-2 

5823.3 

per  cubic  foot.  .  .  . 

156.3 

641.9 

'  ~o          2          f         6          8         10 


8<-ale  of  Feet 

FIG.  245. 


25.  Water-gas.  —  A  great 
deal  of  gas  for  illuminating  and 
power  purposes  is  now  made  by 
the  process  of  intermittent  and 
alternate  blowing  of  air  and 
steam  through  a  thick  bed  of  fuel  in  a  cylindrical  producer  of 
boiler-plate  lined  with  refractory  material.  While  the  process 
may  be  conducted  also  continuously,  the  product  of  the 
continuous  process  is  more  often  called  producer-gas.  The 
fuel  is  blown  by  air  from  below  until  it  becomes  highly 
incandescent;  the  producer  may  be  open  at  the  top,  and  waste 
the  lean  carbonic  oxide  which  comes  off  from  the  top,  or  the 
latter  can  be  caught  and  used.  After  blowing  the  air  as  long  as 
necessary,  in  what  is  called  the  "intermittent"  process,  the 
air  is  shut  off,  and  steam  is  similarly  blown  from  below,  with 


LIBERATION  OF  HEAT  ENERGY.  51 

the  producer  closed  except  at  its  delivery  to  a  gas-holder.  The 
steam  is  dissociated  by  the  incandescent  carbon  into  hydrogen 
and  oxygen,  and  the  latter  unites  with  the  carbon  as  in  the  air- 
producer,  to  be  reduced  to  carbonic  oxide.  The  hydrogen  passes 
out  without  further  chemical  reaction.  The  process  may  be 
made  continuous  by  blowing  air  and  steam  together.  Since  the 
usual  steam-jet  blower  will  carry  the  necessary  air  with  it,  this 


method  is  the  one  in  more  general  use.  This  process  was  intro- 
duced in  1874  by  Mr.  T.  S.  C.  Lowe,  and  is  often  known  generally 
as  the  Lowe  process.  For  illuminating  purposes  this  fuel-gas  is 
more  highly  carburetted  by  sprays  of  hydrocarbon  vapors  (such  as 
naphtha  or  similar  petroleum  products)  which  are  made  a  fixed 
gas  by  later  heating  in  a  superheater. 


THE   GAS-ENGINE. 


Fig.  8  illustrates  what  is  called  in  England  the  Dowson  gas- 
producer,  which  belongs  to  this  class.     Its  product  is  sometimes 


FIG.  9. 

known  in  America  as  semi-water-gas.     Its  analysis  is  given  in 
parag.  29 


LIBERATION  OF  HEAT  ENERGY.  53 

The  ash-pit  B  is  closed  and  air  and  st'eam  are  forced  through 
N  and  up  through  the  mass  of  anthracite  or  coke  which  fills  the 
producer-chamber.  The  feeding  is  done  through  the  hopper  A' 
by  means  of  its  double  lid  and  air-lock  action.  The  gas  passes 
up  through  the  coke-scrubber  into  the  holder  K. 

A  French  form  of  water-gas  producer  is  known  as  Lencauchez'. 
Its  object  is  to  improve  on  the  Dowson  type  by  saving  waste 
\eat,  and  render  it  available  for  coals  having  some  tendency 
<o  fuse  together  from  the  presence  of  tarry  matters  (Fig.  9). 
The  hanging  bridge  E  forces  the  gases  above  the  middle  of  the 
fuel-bed  to  pass  downwards  before  escaping  to  the  flue  F,  and 
"to  out  to  the  holder  through  the  passage  /.  The  annular  chamber 
H  is  a  steam-boiler,  whose  water  cools  the  outflowing  gases,  and 
whose  steam  entering  the  chamber  G  meets  with  the  air  from  a 
blower  through  the  pipe  L,  and  the  combined  air  and  steam  are 
forced  through*  the  pipes  M  into  the  closed  ash-pit  and  so  up 
through  the  fuel.  The  descent  of  the  distilled  gas  through  the 
hot  fuel  before  passing  out  is  the  feature  which  is  expected  to 
break  up  the  tarry  elements  of  the  distillation.  Lencauchez'  gas 
analysis  shows: 

Hydrogen,                   H 18.34 

Olefiant  gas,                C2H4 1.25 

Hydrocarbons,             C4H4 1.55 

Carbonic  oxide,           CO 27.32 

Carbonic  acid,             CO2 3-6o 

Sulphur  dioxide,          SO2 0.04 

Hydrogen  disulphide,  H2S 0.06 

Nitrogen,                     N 47-84 

Dowson  gas  has  a  calorific  value  averaging  150  B.T.U.  per 
cubic  foot,  while  the  true  water-gas  should  have  290. 

Fig.  10  is  a  general  elevation  of  a  complete  producer  plant 
for  power  purposes,  with  economizer,  scrubber,  and  gas-holder. 

A  comparison  of  water-gas  and  anthracite  producer-gas  might 
take  the  following  form: 


54 


THE  GAS-ENGINE. 


LIBERATION  OF  HEAT  ENERGY.  55 

First-class  carburetted  water-gas,  made  with  4.-J  gallons  of 
Lima  oil  per  1000  feet  of  gas,  C.P.  26^,  contains  730  H.U.  per 
cubic  foot. 

One  pound  of  anthracite  coal  (C  85  per  cent,  HC  5  per  cent, 
ash  10  per  cent)  will  make  about  90  cubic  feet  of  gas  of  follow- 
ing composition:  CO  27  per  cent,  H  12  per  cent,  CH4  1.2  per  cent, 
CO2  2.5  per  cent,  N  57  per  cent.  This  gas  contains  about  137 
H.U.  per  cubic  foot.  Therefore  17  cubic  feet  of  carburetted 
water-gas  are  equal  in  heat-units  to  gas  from  one  pound  of 
anthracite. 

1000  feet  C.W.  gas  equals  gas  from  59+ pounds  anthra- 
cite. 

The  Lencauchez  feature  of  drawing  the  products  of  distil- 
lation through  the  bed  of  fuel  to  gasify  the  tarry  matters  may  be 
carried  further,  so  that  the  gas  passes  downward  through  the 
entire  fuel  mass  except  where  free  oxygen  is  present  for  combus- 
tion. Such  producers  are  called  inverted-combustion  producers 
and  to  it  belong  the  Deschamps  and  the  Fange-Chavanon 
types  illustrated  in  Fig.  250.  In  the  sections  of  European  de- 
signs given  in  Figs.  248-250  will  be  noted  the  differences  in 
detail  involved  where  the  attention  of  the  creator  has  been 
directed  to  secure  advantages  not  realized  in  competing  forms. 

2$a.  Aspirating  Producers. — The  gas  producers  discussed  in 
paragraphs  25  and  24  operate  by  pressure  of  air  or  steam  or 
both  in  the  closed  ash-pit,  and  the  tension  within  them  is  above 
the  atmospheric  pressure.  This  principle  of  action  entails  an 
auxiliary  plant  for  making  steam  or  producing  air-pressure,  and 
the  heat  or  fuel  to  operate  this  auxiliary  equipment  should  prop- 
erly be  charged  to  the  heat  or  fuel  account  of  the  producer  itself. 
Such  auxiliary  plant  makes  the  apparatus  cumbrous,  and  when 
the  quantity  of  gas  required  is  small,  as  for  small  gas-engines, 
it  becomes  disproportionately  costly.  The  system  also  requires 
a  gas-holder,  as  shown  in  Figs.  8  and  10,  since  the  production 
of  gas  is  controlled  by  the  rapidity  of  combustion  at  the  base 


56  THE  GAS-ENGINE. 

of  the  producer,  and  this  action  in  turn  by  the  jet  in  the  ash-pit 
and  not  by  the  consumption  of  gas  by  the  motor  or  motors.  The 
holder  must  therefore  act  as  an  accumulator  between  the  producer 
and  a  variable  demand  for  gas. 

For  isolated  plants  of  relatively  small  capacity,  or  where  but 
one  gas- motor  is  to  be  supplied  by  such  a  generator,  it  appeared 
at  once  of  great  importance  to  simplify  the  plant  as  to  bulk  and 
cost  on  the  one  hand,  and  on  the  other  to  make  the  demand  of  the 
engine  the  governing  factor  in  the  generation  of  the  gas  from 
the  solid  fuel.  This  has  given  rise  to  the  producer  acting  by 
aspiration,  directly  connected  to  the  suction  inlet  of  the  gas- 
motor,  and  operating  under  a  tension  less  than  atmospheric  pres- 


FIG.  74. 

sure.    These  are  called  aspirating  producers,  and  Fig.   74  will 
illustrate  a  typical  form. 

In  this  arrangement,  as  designed  for  an  isolated  plant,  the 
producer  A  at  the  left  operates  by  air  and  steam,  which  are  drawn 
into  the  ash-pit  below  the  fire  by  the  diminished  pressure  above 
the  bed  of  combustible.  The  fuel  is  charged  through  the  top 
as  required.  To  start  the  process  before  the  motor  begins  to 
make  aspirating  strokes  a  small  fan  or  other  air-driving  appa- 
ratus, as  at  F,  must  be  run  by  hand  or  by  stored  or  other  power 
to  start  and  maintain  the  combustion  at  the  base  of  t\ie  producer. 
The  poor  and  lean  gas  of  the  starting  process  will  be  wasted 


LIBERATION  OF  HEAT  ENERGY.  57 

through  an  air-vent  pipe  D  to  the  open  air.  The  generated  gas 
with  the  heat  of  the  producer  and  its  combustion  process  is  led 
into  a  steam-generator  B,  which  is  in  effect  a  multitubular  boiler. 
Water  is  delivered  into  the  top  of  this  boiler  at  atmospheric  pressure, 
and  is  made  into  steam  at  low  pressure  by  the  heat  of  the  flow- 
ing gas.  The  steam  passes  by  a  pipe  downward  into  the  ash- 
pit of  A  by  the  aspiration  effect  therein,  and  any  excess  of  water 
flows  to  waste  through  an  overflow.  The  gas  passes  from  B  to 
the  scrubber  C,  which  is  filled  with  coke  and  through  the  inter- 
stices of  which  the  gas  rises,  while  the  washing  water  descends. 
The  water  takes  up  and  removes  the  dust  from  the  producer,  and 
catches  the  ammonia  liquor  and  other  impurities  which  water 
will  absorb.  The  gas  then  passes  to  a  receiver  E  of  relatively 
large  cross-section  as  compared  to  the  gas  suction-pipe  of  the 
motor,  so  that  the  strokes  of  the  motor  shall  not  cause  pulsations 
between  the  receiver  and  the  producer.  The  blower  F  has  to 
be  run  from  ten  to  fifteen  minutes  in  a  plant  of  small  size,  and 
after  a  further  fifteen  or  thirty  minutes  of  light  or  empty  running 
of  the  engine  itself  the  producer  will  be  making  gas  enough 
regularly  for  its  full  load.  Of  course  the  vent  D  is  closed  as 
soon  as  the  gas  is  rich  enoujh  in  quality  and  sufficient  in  amount 
to  start  the  engine  by  the  usual  procedure  (par.  162).  Such 
aspirating  producers  can  be  applied  from  the  smallest  capacities 
up  to  300  horse-power  of  the  engines.  It  is  plain  that  in  the 
smaller  sizes,  and  with  the  gentle  pressures  which  prevail,  the 
pitchy  and  caking  coals  are  at  a  disadvantage,  and  the  producer 
works  better  when  the  fuel  is  of  about  a  standard  size,  about 
that  of  a  walnut.  When  the  coal  goes  to  powder  also  with  heat, 
the  passages  for  gas  are  clogged,  and  the  back  pressure  on  the 
motor-cylinder  is  increased  for  its  aspirating  stroke. 

Many  modifications  of  this  typical  form  are  possible,  such  as 
the  use  of  an  open  water-jacket  around  the  incandescent  zone  of 
the  producer,  from  which  the  steam  generated  by  the  heat  shall 


THE  GAS-ENGINE. 


be  led  under  the  fire,  and   the  leading  of  the  water  from  the 
motor-water-jackets  to  both  producer  and  scrubber. 

An  American  arrangement  of  aspiration  or  suction  producer 
is  illustrated  in  Fig.  75.  In  this  type,  the  producer  A  is  a  cylin- 
drical steel  shell  lined  with  fire-brick,  and  fitted  with  a  revolving 
grate.  Between  the  shell  and  the  brickwork  is  an  annular  space 
through  which  the  air  for  combustion  and  reaction  with  the  fuel 
can  pass  from  the  element  B,  together  with  the  steam  vaporized 
therein,  so  as  to  enter  the  producer  at  the  bottom.  This  jackets 
the  producer  on  the  one  hand,  and  warms  the  air  and  heats  the 
low-tension  steam  on  the  other.  The  charging  of  fuel  is  effected 


PRODUCER  A 

SATURATOR  B 

HYDRAULIC  Box  C 

COKE  SCRUBBER  D 

SAWDUST  SCRUBBER  E 


FIG.  75. 

by  one  or  two  charging-hoppers,  through  tubes  and  valves.  A 
central  collecting-bell  hanging  from  the  top  receives  the  gas,  and 
serves  also  to  keep  the  fuel  at  a  constant  level.  The  bottom 
of  the  producer  is  closed  by  a  water-seal,  so  that  the  fire  can  be 
cleaned  and  the  ashes  and  clinker  removed  without  interrupting 
the  continuous  operation  of  the  plant.  The  element  B  is  called 
the  saturator,  and  is  a  water- jacketed  pipe  through  which  the 
hot  gas  passes,  and  evaporates  the  water  in  the  jacket.  This 
water  is  kept  at  a  constant  level,  and  the  steam  which  is  formed 
is  entrained  by  the  entering  air  and  carried  with  it  to  the  base  of 
the  producer.  In  modifications  of  this  type,  the  evaporator  is 


LIBERATION  OF  HEAT  ENERGY. 


59 


put  on  the  top  of  the  producer.  At  C  is  a  hydraulic  box  acting 
as  a  check-valve  or  seal  to  prevent  gas  from  backing  up  into  the 
producer.  The  elements  D  and  E  are  scrubbers.  D  is  the  coke 
scrubber,  necessary  in  any  case,  and  E  is  a  sawdust  scrubber, 
filled  with  trays  on  which  sawdust  or  similar  material  acts  to 
remove  the  last  vestiges  of  fine  ash  or  other  solid  matter  which 
may  have  passed  the  coke  scrubber  D.  If  the  gas  is  clean  enough 


FIG.  246 — Tangye  Sucticn  Producer. 

without  the  use  of  the  second  scrubber,  its  use  can  be  omitted. 
From  here  the  gas  is  piped  to  the  engine. 

If  a  typical  producer  of  this  sort  be  applied  to  supply  gas  to 
an  engine  of  40  horse-power  with  anthracite  or  coke  as  fuel,  it  can 
reasonably  be  expected  to  give  a  horse-power  on  i  pound  of 
fuel.  In  ten  hours  it  will  therefore  use  only  400  pounds  of  fuel  or 
one-fifth  of  a  ton,  and  at  ordinary  prices  of  coal  this  will  be 
much  less  than  a  dollar  a  day  for  fuel  expense  of  the  plant. 

Fig.  246  shows  an  English  typ3  of  aspi.a  ing  producer  with 
attached  scrubber,  the  motor  drawinj  gas  from  the  down-take 
at  the  right  hard. 


Benier. 


Phoenix. 


Bollinckx. 


A.  Taylor. 


Pintsch.  Hffle.  Weidenfeld. 

FIG.  248.— FOREIGN  SUCTION  PRODUCERS. 


Goebels. 


Kinderlen. 


Otto-Deutz. 
FIG.  249. — FOREIGN  SUCTIO?I  PRODUCERS. 


Pierson. 


Benz. 


Riche  Combustion. 


Riche  Wood  Distillation 


Fange  Chavanon  Inverted  Combustion.          Deschamps  Inverted  Combustion. 
FIG.  250. — FOREIGN  PRODUCERS. 


&4  THE  GAS-ENGINE. 

26.  Coal-gas    or  Illuminating-gas. — The    ordinary  gas  used 
in  cities  and  large  towns,  and  which  was  universal  previous  to 
the  introduction  of  water-gas,  is  made  by  distilling  bituminous 
coal  in  retorts.     These  retorts  are  long  semi-cylindrical  tubes 
holding  each  from  160  to  300  pounds  of  caking  bituminous  coal 
—often  enriched  by  some  cannel  coal — under  and  around  which 
the  heat  from  a  coke  fire  is  maintained.     The  vapors  distilled 
off  become  a  fixed  gas  by  being  passed  through  that  part  of  the 
distilling  apparatus  which  is  kept  at  a  white  heat.     Other  features 
of  the  process  involve  the  methods  for  condensing  tarry  and 
offensive  vapors  and  for  cleansing,  which  are  aside    from  the 
present  purpose.      The  products  of  distillation    of    100  pounds 
of  ordinary  gas-coal  are  usually 

Coke 64      to  65     pounds 

Purified  gas 15      "  12 

Ammonia  liquor. 10      "12 

Tar 6.5  "    7.5       " 

Loss  and  impurities 4-5"     3-5       " 

100.0     100.0      " 

27.  Acetylene   Gas. — The   gas   C2H2  released   from   calcium 
carbide  by  addition  of  water  is  as  yet  of  no  significance  for  large- 
scale  heating,  but  has  been  much  examined  for  use  in  motor 
carriages  and  elsewhere  where  gas-power  in  small  bulk  is  the 
prerequisite.     One  pound  of  calcium  carbide  with  a  little  over 
half  its  weight  of  water  will  liberate  5f  cubic  feet  of  gas.     It  has 
a  heat  capacity  of  18,260  to  21,492  B.T.U.  per  pound  or  1500  to 
1624  per  cubic  foot,  and  weighs  0.0725  pound  per  cubic  foot  or 
occupies  14^  cubic  feet  to  the  pound.    It  requires  12  J  volumes  of 
air  to  burn  it,  which  is  usually  raised  to  14  or  15  in  practice.    It 
has  been  compressed  to  a  liquid  at  68°  F.  by  a  pressure  of  600 
pounds  per  square  inch. 

Acetylene  ignites  at  510°  F.  in  proper  mixtures  with  air,  and 
has  a  specific  heat  about  0.245  ^or  its  products  of  combustion 
at  constant  volume.  Some  very  complete  experiments  by  Mr. 


LIBERATION  OF  HEAT  ENERGY.  65 

Frederick  Grover  of  England  between  1898  and  1901,  to  be 
referred  to  later  (Chapter  XIX),  showed  that  whereas  a  mix- 
ture of  9  parts  coal-gas  to  i  of  air  was  required  to  give  an 
initial  pressure  of  180  pounds  in  the  cylinder,  after  compression 
to  30  pounds,  the  same  pressures  resulted  from  acetylene 
with  30  to  i.  With  11.7  to  i  and  the  same  compression  he 
observed  352  pounds  pressure  to  result  from  ignition.  If  the 
thermal  efficiency  for  acetylene  be  taken  at  30  per  .cent/  6.1 
to  6.3  cubic  feet  of  gas  would  be  required  per  H.P.  per  hour. 
The  ignition  temperature  is  low;  the  transmission  of  flame  in 
the  mixture  is  rapid;  the  combustion  temperature  and  conse- 
quent mechanical  energy  are  high.  For  quantitative  results  the 
reader  is  referred  to  Chapter  XIX. 

28.  Blast-furnace  Gas. — Since  the  first  experiments  in  1895  an 
increasing  use  is  continually  found  for  the  gas  discharged  from  the 
top  of  the  blast-furnace  as  a  source  of  motive  power.  Less  than 
one-third  of  the  carbon  introduced  into  the  blast-furnace  can  be 
allowed  to  reach  the  state  of  CO2  in  order  to  maintain  the  reduc- 
ing action  demanded  for  the  chemical  reactions  on  the  iron  ore. 
Hence  the  discharged  gas  consists  largely  of  carbonic  oxide 
(CO),  although  it  is  probably  the  leanest  form  of  fuel-gas  which 
is  used,  running  about  100  B.T.U.  per  cubic  foot.  There  is  a 
small  proportion  of  CH4  from  the  dry  distillation  of  the  coal 
before  it  gets  far  down  the  shaft,  and  hydrogen  from  moisture 
in  the  charge.  The  CO2  is  due  to  imperfections  in  the  reduction 
process  upon  the  ore,  from  calcination  of  the  limestone  used  as 
flux  and  from  union  of  CO  with  oxygen  from  the  ore  at  temper- 
atures too  low  to  be  decomposed  again.  German  analyses  give 
25  to  30  per  cent  of  CO,  55  to  60  per  cent  of  N,  12  per  cent  of 
CO 2,  3  per  cent  of  hydrocarbons.  The  CO  burns  with  a 
transparent  blue  flame  of  low  calorific  power,  taking  therefore  a 
large  volume  of  gas  when  used  to  make  steam  for  power.  When 
the  gas  is  used  in  gas  engines  on  the  other  hand  the  ineffectiveness 
disappears,  and  a  given  gas  from  a  ton  of  pig-iron  made  will 
supply  five  times  the  power  obtained  when  used  indirectly  under 
boilers.  German  computations  state  that  the  gas  per  ton 


66 


THE  GAS-ENGINE. 


of  pig-iron  when  used  to  make  steam,  will  give  an  average  of 
400  H.P.  The  usual  computation  calls  for  28  per  cent  of  the 
gas  for  preheating  the  blast  for  the  furnace  and  10  per  cent  in 
loss  and  waste,  leaving  the  balance  or  62  percent  for  power. 
The  power  gas  may  be  all  used  in  gas-engines,  or  part  in  making 
steam  and  part  in  gas-engines,  or  all  may  be  used  in  making 
steam.  Taking  as  an  accepted  value  for  the  cubic  feet  of  gas 
per  ton  of  pig-iron  the  total  of  163,590  with  a  calorific  power 
of  101  B.T.U.  per  cubic  foot,  the  proportions  and  distribution 
would  be  as  follows: 

I.   ALL   GAS   ENGINES. 


Per  Cent. 

Cubic  Feet. 

Cubic  Meters. 

Heating  the  blast 

28.06 

4<?,QO3 

I   3OO 

\Vaste  in  pipes,  etc  

IO 

16,348 

463 

Driving  blast-engines  

10.87 

17,706 

"?O4 

Balance  available  for  other  purposes 

5!-°7 

83>543 

2,366 

100.00 

163,590 

4,633 

II.   PARTLY   STEAM,   PARTLY   GAS   ENGINES. 


Heating  the  blast     

28.06 

4?,  QO3 

I,3OO 

Wastes  

IO 

16,348 

463 

Driving  blast  engines 

30    28 

64.264 

I  820 

Balance  available                        .    ... 

22    66 

27,075; 

I,O£O 

III.   ALL   STEAM   ENGINES. 


Heating  the  blast           

28.06 

4S.QO? 

I.3OO 

Wastes                         

IO 

16,348 

463 

<?Q     28 

64,264 

I  820 

22    66 

37,07? 

I.O^O 

The  financial  possibilities  of  the  first  table  will  be  governed 
by  the  possibilities  of  sale  in  the  neighborhood  of  the  surplus 
power  in  the  form  of  electrical  or  other  energy. 


LIBERATION  OF  HEAT  ENERGY.  67 

The  objections  which  have  been  urged  against  using  the 
blast-furnace  gases  as  producer  gases  for  power  have  been: 

1.  The  dirt  which  they  contain. 

2.  Their  high  temperature. 

3.  The  danger  to  the  men  from  their  asphyxiating  effect  at 
leaks  and  joints. 

4.  Their  low  heating  value. 

5.  The  irregular  supply  of  heat  energy  due  to  fluctuations 
of  composition  and  quantity. 

The  dust  from  the  blast  furnace  seems  to  be  of  two  sorts. 
One  is  heavy,  consisting  of  particles  of  ore,  coke,  and  lime  carried 
over  in  the  current  and  which  will  be  dropped  by  the  expedient 
of  lowering  the  velocity  of  flow  at  some  point  or  by  the  passage 
of  the  gas  over  water  at  such  point.  These  dust-catchers  have 
been  used  and  have  been  successful  in  the  plants  where  the  gas 
is  burnt  under  boilers.  The  other  dust  is  fine  and  impalpable, 
resembling  flour  in  consistence,  and  is  deposited  by  the  metallic 
vapors,  containing  also  clay  and  lime.  In  amount  it  varies 
from  3  to  5  grams  in  the  cubic  meter,  in  ordinary  gases,  the 
difficulty  increasing  greatly  when  zinc  dust  or  similar  oxides 
are  also  present.  Two  general  systems  are  in  use,  which  may 
be  distinguished  by  the  two  names  of  static  and  dynamic.  The 
static  systems  use  stationary  devices  such  as  scrubbers  and 
purifiers,  in  which  coke,  sawdust,  or  moss  are  used  as  with  pro- 
ducer gas,  in  connection  with  sieves  or  trays,  acting  as  filters, 
with  water  to  wash  the  gas  in  transit  and  to  remove  the  incon- 
venient excess  of  temperature.  In  the  dynamic  system,  centri- 
fugal fans  are  used  with  jets  of  water,  either  singly  or  in  series 
with  a  long  pipe  for  settling  purposes  between,  or  a  coke 
filter  may  be  used  after  the  fan.  In  such  a  plant,  in  England, 
the  dust  is  1.8  grams  per  cubic  meter  before  reaching  the  fan, 
and  0.4  gram  after  leaving  it.  Five  hundred  gallons  of  water 
per  hour  are  injected,  but  the  water  can  be  used  over  and  over 
again.  The  fan  has  to  be  cleaned  once  in  two  weeks.  The 
trouble  from  the  dust  at  the  engines  is  both  from  clogging  of 
passages  and  the  combination  with  the  lubricating  material,  but 


68  THE  GAS-ENGINE. 

even  more  than  this  the  presence  of  the  grit  causes  annoying 
abrasion  of  valve  faces  and  cylinders  and  pistons. 

Vertical  engines  offer  advantage  over  horizontal  ones  from 
this  cause  because  the  grit  does  not  lie  on  the  surface  over  which 
the  piston  moves. 

The  solution  of  the  cleaning  problem  which  seems  to  be 
satisfactory  in  the  dynamic  type,  is  also  the  solution  of  the  incon- 
venient heat  problem.  The  cooling  injection  water  can  be 
used  over  and  over  again  with  adequate  reservoirs  or  tanks. 

The  physiological  effects  of  blast-furnace  or  producer  gas 
rich  in  carbon  monoxide  (CO),  are  of  special  difficulty  to  meet, 
because  on  coming  into  contact  with  the  blood  in  the  lungs, 
the  necessary  process  of  oxygenation  not  only  does  not  take  place, 
but  a  curiously  stable  compound  seems  to  be  found  in  the  blood 
itself  which  is  reacted  upon  by  the  oxygen  of  the  air  with  reluc- 
tance. As  this  reaction  of  the  carbon  monoxide  takes  place 
even  in  the  presence  of  oxygen,  a  poisoning  can  occur  even  in 
the  open  air.  Hence  the  physiological  effects  are  of  two  classes : 
the  slow  progressive  type  and  the  rapid  though  gradual  asphyx- 
iation. The  slow  poisoning  evidences  itself  in  pains  in  the 
head ;  pallor,  due  to  anaemia ;  lassitude ;  muscular  weakness,  and 
ultimate  paralysis,  general  and  local.  The  end  is  an  asphyxia- 
tion, if  the  man  is  not  removed  from  the  influence  of  the  gas. 
The  rapid  asphyxiation  process  is  revealed  by  headache  and 
nausea,  vertigo,  congestion  at  the  temporal  blood-vessels,  dim- 
ness of  vision,  and  mental  depression.  A  strong  desire  to  sleep 
succeeds,  and  if  the  victim  can  get  fresh  air  at  this  stage  he 
usually  comes  out  all  right.  A  little  later  under  the  influence  of 
the  poison,  paralysis  of  the  lower  limbs  follows,  and  then  coma 
and  death.  If  the  asphyxiation  is  discovered  and  antagonized 
in  time,  only  a  severe  headache  remains  after  it  in  most  cases. 
A  little  later  than  this,  however,  the  oxygen  of  the  air  is  too 
feeble  to  recover  the  victim,  and  a  current  of  pure  oxygen  from 
a  pressure  tank  delivered  to  a  respirating  orifice  in  a  mask  over 
the  face  is  required.  If  necessary  the  same  methods  of  pro- 
ducing respiration  artificially  or  mechanically  must  be  used,  as 


LIBERATION  £)F  HEAT  ENERGY.  69 

would  be  applied  to  those  apparently  drowned:  the  chest  cavity 
is  alternately  expanded  and  contracted  by  drawing  the  arms 
upward  over  the  head  and  they  are  then  forced  downward  and 
pressed  inward  upon  the  chest  as  the  patient  lies  upon  his  back. 
The  movements  are  made  slowly  and  decisively  fifteen  or  twenty 
times  per  minute,  and  kept  up  if  necessary  for  several  hours, 
and  heart  action  stimulated  by  external  heat,  friction,  and  pun- 
gent vapors  in  the  nostrils.  These  difficulties  with  blast-furnace 
gas  should  be  no  worse  than  with  producer  gas  except  from  the 
scale  on  which  they  are  carried  on,  and  from  the  danger  that  in 
furnace  plants  the  pressure  of  production  and  the  financial  loss 
due  to  stoppage  will  postpone  the  overhauling  necessary  to  keep 
the  plant  up  to  conditions  as  respects  the  cleanness  of  the  engines 
and  the  prime  quality  of  joints  and  packings.  Operatives  object 
to  respirators  and  will  discard  them;  incessant  vigilance  and 
frequent  inspections  from  the  superintendence  class  above  them 
is  the  only  safeguard.  The  gas  is  colorless  and  without  effect 
on  the  nerves  of  smell  or  taste  when  pure. 

The  fourth  alleged  difficulty  from  low  heating  value  is  without 
significance,  or  does  not  exist.  The  cylinder  volume  of  the 
engine  is  greater,  but  the  poor  gas  is  as  efficient  per  heat  unit  as 
the  richer,  and  a  greater  compression  ratio  is  possible  without 
inconvenient  pre-ignitions.  Gases  as  lean  as  87  B.T.U.  per 
cubic  foot  have  been  successfully  used. 

The  irregular  quality  and  quantity  of  the  fuel  supply  dis- 
appears as  the  number  of  furnaces  in  the  plant  is  increased.  It 
has  not  been  found  a  significant  factor  of  trouble.  If  thought 
advisable  a  holder  of  sufficient  capacity  may  be  introduced 
between  blast  furnaces  and  engine  plant,  acting  as  an  accumu- 
lator and  equalizing  both  quality  and  quantity.  An  independent 
producer  may  also  be  made  to  serve  this  same  accumulator  if 
thought  desirable.  Lighting  and  power  gases  from  any  source 
are  not  perfectly  uniform  at  all  times. 

If  the  average  heat  capacity  or  calorific  power  per  pound  of 
blast-furnace  gas  be  called  1283  B.T.U.  and  the  percentage  of 


THE  GAS  ENGINE. 


heat  energy  effective  in  the  gas  be  from  20  per  cent  to  30  per 
cent,  as  is  usual,  then  there  will  be  required 


33,000X60 
778 


X 


7-93 


pounds  of  gas  per  H.P.  per  hour  if  an  efficiency  of  25  be  assumed. 
Reducing  this  to  cubic  feet  per  minute,  with  a  piston  speed  of 
800  linear  feet  per  minute  in  a  two-stroke  cycle  engine,  with  a 
stroke  one  and  a  half  diameters,  it  gives  an  accepted  figure  of 
four  cubic  feet  per  minute  per  H.P.  Fig.  n  shows  a  design  of 
engine  for  utilizing  blast-furnace  gas,  originated  by  Mr.  Chas. 
H.  Morgan  of  Worcester,  Mass.  By  using  vertical  cylinders  he 
diminished  the  abrasive  action  of  grit  or  dust  in  the  gas,  and 
by  the  beam  mechanism  he  diminished  the  tendency  of  the  piston 
to  "cock"  or  produce  oblique  pressure  in  the  cylinder. 


FIG.  ii. 

Analyses  of  blast-furnace  gas  will  be  found  among  the  follow- 
ing tables. 

Gases  from  coke-ovens  are  also  available  sources  of  fuel-gas 
for  engines.  After  the  first  eight  hours  of  the  coking  process 
gas  appears  from  the  top  of  the  oven,  and  continues  to  be  evolved 


LIBERATION  OF  HEAT  ENERGY. 


until  it  reaches  a  maximum  at  the  end  of  the  second  day,  and 
then  gradually  diminishes  until  the  oven  is  discharged  at  the  end 
the  third  or  on  the  fourth  day.  With  the  maximum  output  of 
gas  at  40  per  cent  from  one  oven,  the  average  will  be  20  per  cent, 
with  a  heating  value  per  cubic  foot  averaging  60  B.T.U.,  with 
the  maximum  of  120  and  the  minimum  of  zero  at  the  end  when 
the  constituents  are  CO2  and  N.  Both  blast-furnace  and  coke- 
oven  gases  permit  and  demand  much  higher  compressions  to 
secure  certain  ignition  of  the  lean  mixture.  (Pars.  152,  202.) 

Retort  coke-oven  gas  should  also  be  mentioned  here,  which 
has  a  calorific  value  from  550  to  750  B.T.U.  Plants  of  con- 
siderable size  are  in  operation  both  in  America  and  Europe, 
particularly  in  Westphalia  and  in  Austria. 

29.  Tables  of  Compositions  and  Properties  of  Gases. — 
Of  the  various  kinds  of  gas  referred  to  in  the  foregoing  para- 
graphs, water-gas  has  the  highest  theoretical  temperature  of 
combustion — 4850°  F.  Producer-gas  gives  3441°.  The  natural 
gas  and  coal-gas  give  nearly  the  same  theoretical  combustion 
temperature,  but  vary  greatly  in  calorific  value  with  varying  con- 
ditions. 

COMPOSITION  OF  GASES  BY  VOLUME.* 


Findlay,  O. 
Natural  Gas. 

Coal-gas. 

Water-gas. 

Penna.  Steel- 
works Pro- 
ducer-gas. 

Hydrogen. 

2    18 

46  oo 

Marsh-gas. 

02    60 

40  oo 

Carbonic  oxide.  . 

O     ^O 

6  oo 

.uu 

O    31 

^o-Du 

Carbonic  acid  . 

o  26 

o  ^o 

A       OO 

Nitrogen   .    . 

3  61 

I     ^O 

2    OO 

1  ou 

Oxvgen     ... 

O    3-1 

o  ^o 

O    ?O 

Water-vapor    .        .    . 

o  oo 

I     ^O 

I     ^O 

Sulphydric  acid  .  .    .    . 

o  20 

i.^w 

IOO.OO 

100.00 

100.00 

IOO.OO 

*  The  values  for  water-gas  in  this  table  are  for  the  uncarbureted  product,  usually  known  as 
*'  blue  "  gas).  The  analysis  for  producer-gas  is  for  an  unusually  lean  product  In  modern  practice 
it  is  made  richer. 


THE  G4S-ENG1NE. 


COMPOSITION  OF  GASES  BY  WEIGHT. 


Hydrogen.     ........... 

0.268 

8.21 

5.471 

O.A=,& 

IVIarsh-gas.   .    ......... 

oo.  383 

S7-2° 

I  .92,1 

i  .8^1 

Carbonic  oxide 

o  8;? 

1C  .02 

,      '° 
76.041 

2<    OQ< 

Olefiant  gas 

o  c^i 

IO.OI 

O.OOO 

o.ooo 

Carbonic  acid 

O.7OO 

1  .07 

10.622 

2.517 

Nitrogen 

6.178 

7.7? 

v^so 

69.413 

Oxvsren 

0.666 

i  .43 

0.965 

o.ooo 

\Vater-vapor.        .    . 

o.ooo 

2.41 

1.630 

0.686 

Sulphydric  acid  

0.417 

^ 

IOO.OOO 

100.00 

IOO.OOO 

IOO.OOO 

TABLE  OP  RELATIVE  COSTS  OF  GASES  PER  MILLION  B.T.U.  WHICH  THEY  ARE 
THEORETICALLY  ABLE  TO  PRODUCE. 

Cents  per 
MilHon  B.T.U. 

Coal-gas 734,976  units,  costing  20.00  cents 27.21 

.Water-gas 322>346     "  "       10.88      "    33.75 

Producer-gas 117,000      "          "         2.58     "    22.05 

Approximately  30,000  cubic  feet  of  gas  have  the  heating  power  of  one  ton 
of  coal. 


COMPARATIVE  COMPOSITION  OF  GAS. 


•  • 

Water- 

Produc 

er-gas. 

Findlay,  O. 

gas. 

Anthrac. 

Bitum. 

CO     

O    sO 

6  o 

AC    o 

H  

2    l8 

4.6    O 

*  I  -u 

•*/  -u 

CtL. 

02    60 

4.O    O 

2    O 

C,H,  . 

O    31 

4O 

CO,.. 

»i 

o  26 

O    ^ 

4.    O 

2     C 

2    ^ 

N  

3.61 

I    e 

2    O 

r  7    o 

c6  2 

O  

O.  34 

o.  5 

o  5 

O    3 

O    ^ 

Vapor 

T    r 

T    r 

Pounds  in  1000  cu.  ft        ... 

AC     6O 

•53    O 

AC    6 

65  6 

6c  o 

Heat-units  in  1000  cubic  feet.  . 

1,100,000 

73SiQoo 

322,000 

I37.4SS 

uj-y 
156,917 

LIBERATION  OF  HEAT  ENERGY. 
PRODUCER-GAS  FROM  ONE  TON  OF  COAL. 


73 


Analysis  by  Vol. 

Per  Cent. 

Cubic  Feet. 

Lbs. 

Equal  to 

ro       

25-3 
9-2 

3-1 
0.8 

3-4 
58.2 

12,077.76 
4,069.68 
1,050.24 
4,463-52 
76,404.96 

2,451.20 
63-56 
174.66 
77-78 
519.02 
5A59-63 

1,050.  50  Ibs. 
63-56     ' 
174.66     ' 
77.78      ' 
141-54     ' 

7>35°-i7 

C  +1400.  7  Ibs.  O 
H 
CH4 

air 

H        

CIL. 

C,H4. 

CO  

N  (by  difference) 

100.  0 

131,280.00 

8,945-85 

RELATIVE  CALORIFIC  VALUES. 


By  Weight. 

By  Volume. 

Sp.  Gr.* 

Natural  gas  

Coal-gas 

1,000 

Q4.Q 

1,000 

666 

Water-gas 

2Q2 

ail  2 

Producer-gas 

76  c 

1  30 

w-y/^ 

*  With  air  as  i  .00. 

The  heating  value  of  New  York  City  illuminating-gas,  as  given 
by  Mr.  E.  G.  Love,  per  cubic  foot  at  6c°  F.  and  barometer  at  30 
inches  will  range  715,  692,  725,  732,  691,  738,  735,  703,  734,  730, 
731,  727,  which  will  average  at  721.  Probably  710  would  be 
more  nearly  representative  of  average  good  quality.  The  coal- 
gas  of  London,  with  16  to  17  candle-power,  has  a  calorific  power 
of  668  units  per  foot  and  costs  from  60  to  70  cents  per  thousand 
cubic  feet.  It  ignites  at  temperatures  of  750°  to  800°  F.  with 
proper  mixtures  of  air. 

In  the  accompanying  large  table  is  gathered  a  summary  of 
data  on  the  gaseous  fuels  which  have  been  treated  in  the  fore- 
going paragraphs.  These  will  be  useful  in  computing  quanti- 
ties hereinafter  required,  and  for  convenience  of  reference  it  can 
be  made  to  include  also  columns  deducible  from  the  data  re- 
corded. This  table  should  form  the  basis  of  intelligent  and 
thorough  design,  and  is  believed  to  be  of  the  importance  which 
is  given  to  it  by  its  comprehensive  character.  In  comment 
thereon  and  to  demonstrate  its  utility  it  should  be  observed : 


74  THE  GAS-ENGINE. 

1.  It  has  been  arranged  with  some  reference  to  the  economic 
significance  of  the  various  sources  of  gas.     The  retort  or  city 
gas  made  primarily  for  illuminating  purposes  has  been  put  quite 
low  in  the  list,  since  producer  or  fuel  gas  proper  will  be  made 
for  power  purposes  and  distributed  by  mains  in  the  cities  of  the 
future,  when  the  development  of  the  internal-combustion  motor 
shall  justify  the  necessary  investment  of  capital. 

2.  The   atomized   carburetor  gas   is   the   carbureted-air  gas 
used  in  car-lighting,  in  the   motor  vehicle  for  propulsion  and 
elsewhere,  where  the  hydro-carbons  come  from  alcohol,  gasoline 
or  kerosene.     It  might  be  called  "oil-gas  "  with  equal  propriety. 
The  only  limitations  to  be   observed   are   that   the   carburetors 
should  not  require  vacuum  to  make  them  effective  with  gasoline 
or  kerosene,  and  the  kerosene  should  not  be  injected  in  liquid 
state  to  be  vaporized  by  heat  or  compression. 

3.  If  the  fuel  actually  used  in  any  case  has  only  a  partial 
analysis  made,  as  by  the  Orsat  or  other  analytical  method  (par. 
38),  no  considerable  error  will  be  made  by  using  the  data  for  the 
gas  which  comes  nearest  to  these  known  figures  in  the  table. 
Where  CO,  CO2  and  O  have  been  found,  and  the  gas  process 
of  manufacture  is  known,  the  other  values  will  lie  within  the 
limits  given.     Where  only  the  process  of  manufacture  is  known 
but  no  analysis  is  available,  then  the  high  and  low  limits  should 
be  taken  for  the  gases  of  that  sort,  and  these  computations 
used  as  the  two  limits  within  which  correct  results  will  fall. 

4.  In  using  the  table  for  computations  on  any  gas  or  com- 
pound not  listed  in  it,  the  method  to  be  followed  is  identically 
that  used  in  making  the  table  itself.     From  some  authentic  and 
reliable  source  of  reference  and  record  the  constants  for  each 
element  are  to  be  taken.     Then  by  the  method  given  in  paragraph 
14,   the   quantity  by  weight  of  oxygen  required   for   complete 
chemical  union  or  combustion  is  to  be  computed,  and  the  volume 
of  air  to  furnish  that  weight  of  oxygen  will  be  4.75  times  the 
volume  of  oxygen  required  at  o°   C.     At  62°  the  more  usual 
and  convenient  figure  is  4.8.     Having  then  the  analysis  given  in 


LIBERATION  OF  HEAT  ENERGY. 


75 


cubic  feet  of  each  element  in  one  cubic  foot  or  one  hundred  or 
one  thousand  cubic  feet,  this  figure  is  multiplied  by  the  B.T.U. 
of  each  such  element  from  the  standard  data,  both  high  values 
and  low.  These  elementary  values  added  together  give  the 
total  B.T.U.  high  and  low  per  unit  of  the  compound  gas 
under  computation.  Then  the  cubic  feet  of  air  per  element  is 
found  by  multiplying  the  volume  of  each  elementary  gas  by  the 
cubic  feet  of  air  required  for  its  combustion.  Adding  these 
together  the  total  is  the  cubic  feet  of  air  for  the  combustion  of 
the  unit  of  gas.  It  must  be  noted  that  any  oxygen  present  in 
the  gas  acts  negatively  on  the  cubic  feet  of  air  required,  since 
by  its  presence  it  renders  unnecessary  the  admission  of  external 
air  to  satisfy  the  hydrogen  and  carbon.  The  volume  of  oxygen 
multiplied  by  4.8  is  to  be  added  therefore  with  a  minus  sign,  or 
is  to  be  subtracted. 

5.  The  ratio  of  the  mixture  of  air  and  gas  to  the  calorific 
power  is  found  by  dividing  the  figure  in  columns  n  and  12, 
respectively,  by  the  figure  in  column  13  increased  by  one:  that 
is  the  total  cubic  feet  of  air  is  increased  by  one  cubic  foot  of  gas 
to  form  the  mixture,  and  the  ratio  this  bears  to  the  B.T.U.  per 
cubic  foot  high  and  low  are  the  quantities  in  columns  14  and  15. 
The  lower  value  of  these  in  column  15  has  a  very  important 
significance  in  design  of  cylinders  for  a  given  power,  since  the 
mixture  in  the  cylinder  must  have  the  quantity  of  oxygen  com- 
puted and  supplied  in  order  that  the  combustion  of  fuel  may  be 
complete.     No  more  fuel  can  be  gotten  in  per  cubic  foot  of 
cylinder   volume   without   wasteful    (because   incomplete)    com- 
bustion from  lack  of  air:  the  fuel  supply  can  be  diminished 
without  trouble,  but  the  power  of  the  motor  will  be  diminished, 
since  it  receives  less  energy  to  be  converted  into  work  in  each 
cubic  foot  of  mixture. 

6.  If  now  the  quantity  in  column  15  be  multiplied  by  778, 
there  results  the    figure  in  column    16  which  is  the  theoretical 
foot-pound  or  work  capacity  of  such  cubic  foot  of  gas  mixture 
received  into  the  cylinder  of  the  motor  if  it  could  be  completely 


76 


THE  GAS-ENGINE. 


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LIBERATION  OF  HEAT  ENERGY. 


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78 


THE  GAS-ENGINE. 


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LIBERATION  OF  HEAT  ENERGY. 


79 


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IO 

NO 

CO  NO    CM    co 

to  -^t  CNI  NO 

ON  ON  ON  ON 

• 

ON 
00 

00    co  O  NO 

CM      CO    IH      CM 

CM     CM     CM    CM 

NO 

M 

^-  ON  10  •<*• 

00  00  NO  00 
CM    CM    CM    CM 

1 

a 

^-  to  to  O 

CO  CO  CM     CO 

00 

S 

O      M     1ONO 

H    O  00    »*• 

s 

8 
8 

r^  10  H 

IOOO     CM    t^. 

t^ 

8 

M 

!    !    '.    '. 

; 

:      :  : 

• 

IO    M 

O    co 

•               M     0 

CO 

NO 

o" 

o 

IO 

M 

ON  co  10 

n-oo  ON  t^ 

CO  10  10  CO 

CM 

CM 
•V 

0 
10 

M 

IO  O    l^ 

OO    IO  IO  M 

0 
D 

10 

O 

i 

I     I 

Donkin  

jWater  Gas  uncarbureted, 

:          g; 

ia-s  s'-f 

:  "  "  "  .y 

3                    8 

^-^  ^     ^     ^       r^ 
^~^                      'in 

CO 

'bi 

C 

H 

0 

^ 

'C  w 

<u  cc 

WO 

Ij 

• 

* 

'S 

3 


a 


ea 

^  o  >  > 
*  -I—  -M-eoa 


go  THE   GAS-ENGINE. 

utilized.  This  is  the  same,  therefore,  as  the  work  capacity  of 
each  cubic  foot  of  cylinder  volume  which  is  filled  with  the  mixture 
in  question  at  atmospheric  pressure,  to  undergo  the  transforma- 
tions of  the  cycle  of  operations.  It  can  be  reduced  to  horse- 
power per  minute  by  dividing  by  33,000,  or  per  second  by  dividing 
by  550.  This,  however,  is  a  purely  theoretical  maximum,  and 
must  be  carefully  so  understood.  To  make  it  practical  the 
figure  in  column  16  must  be  multiplied  by  a  factor  which  shall 
take  account  of  the  temperature  limitations  necessarily  imposed, 
because  the  mechanical  work  done  is  never  equal  to  the  potential 
total  of  heat  supplied.  Calling  the  ratio  of  the  output  of  work 
to  the  input  of  heat  by  the  accepted  term  "efficiency"  and 
denoting  it  by  E  (par.  47),  then 

T^rc  .  ^       Work  utilized 

Efficiency  =  E  =  — —        — =—  . 
Heat  supplied 

Whence, 

Work    utilized  =  (Heat    supplied)  X  (E). 

There  are  also  practical  losses  in  friction,  and  in  the  other  wastes 
referred  to  in  the  analysis  of  paragraph  ya.  When  a  factor  is 
known  or  found  to  cover  these  losses,  the  value  of  column  16 
multiplied  by  it  will  give  the  power  capacity  for  such  gas  per 
cubic  feet  of  cylinder  volume  supplied  with  the  proper  mixture 
per  unit  of  time.  Since  the  efficiency  value  will  be  shown  to  be 
greater  as  the  compression  possible  in  the  cylinder  is  greater, 
and  compression  is  greater  with  the  lean  or  poorer  mixtures,  it 
will  be  found  that  the  dynamic  value  of  the  various  fuels  differs 
little  per  unit  of  weight.  The  leaner  mixtures  require  larger 
cylinder  volume  to  secure  the  same  power,  as  compared  with 
the  richer  fuels.  The  significance  of  column  16  will  appear 
more  fully  in  the  sequel  (par.  40). 

8.  The  values  in  columns  15  and  16  are  also  too  high  when 
each  cubic  foot  of  the  cylinder  volume  must  contain  also  a  volume 
of  neutral  gases,  not  supporters  of  combustion,  remaining  there 
as  burnt  gases  from  the  previous  combustion  stroke  of  the  motor. 


LIBERATION  OF  HEAT  ENERGY.  8  1 

These  appear  as  adding  a  volume  in  cubic  feet  to  the  denominator 

TT  TT 

of  the  fraction  -  so  that  it  becomes  -  and  therefore 
a  +  i  n  +  a  +  i 

diminishes  the  volume  available  to  receive  fuel  energy.  The 
clearance  volume  may  be  usually  considered  to  be  full  of  burnt 
gas  without  error,  and  the  value  of  n  computed  therefrom.  Any 
mechanical  defects  of  leakage,  mal-adjustment,  excessive  friction 
and  the  like,  will  still  further  lower  the  final  efficiency. 

9.  Since  the  value  in   column   16,  when   multiplied  by  the 
factor  £,  gives  the  mechanical  work  of  a  cylinder  having  a  cubic 
foot  of  volume,  it  must  also  express  the  work  done  by  the  mean 
effective  pressure  over  a  piston  area  of  one  square  foot,  when 
this   pressure   moves  through  one  foot  of  length.     Hence  the 
tabular  value  multiplied  by  E  can  be  considered  as  the  mean 
effective  pressure  for  one  stroke  of  a  1  2-inch  stroke  motor,  having 
one  square  foot  of  piston-area,  which  will  become  the  M.E.P. 
for  pounds  per  square  inch,  by  dividing  by  144.     This  is  the 

same  then  as  multiplying  the  value  in  column  15  by  —£  =  5.4, 

144 

£,  to  give  the  theoretical  M.E.P.  in  pounds  per  square  inch  for  a 
i2-inch  stroke  one-foot-area  engine  using  this  fuel,  and  with  no 
neutrals  in  the  mixture. 

10.  If  the  cylinder  stroke  is  not  one  foot  but  a  number  of  feet, 
Z,  then  the  M.E.P.  will  be  the  value  for  one  foot  of  length  divided 
by  L  or 

M.E.P.  =  SE 


for  a  cylinder  L  feet  long  in  which  L  is  greater  or  less  than  one 
foot.     This  will  be  used  in  detail  in  paragraph  40. 

ii.  Columns  for  calories  per  cubic  meter  and  of  B.T.U.  per 
pound  might  have  been  added  and  left  blank  for  the  convenience 
of  any  to  whom  these  computations  may  at  any  time  prove 
desirable  to  make  for  their  own  use.  It  has  not  seemed  worth 
while  to  burden  the  working  table  with  them.  To  convert 
B.T.U.  per  cubic  foot  into  calories  per  cubic  meter,  multiply  the 
former  by  8.9.  The  temperature  used  in  most  cases  has  been 


82 


THE  GAS-ENGINE. 


Hi! 


°  -: 

"So  0-3-:  0.3 


•s-g 


\O 

O\ 


rO  CO 
CO  O 


to 

OO 


M          M          ro 


^J-    04 

O     O 
OO    to 


o 

to 


(N  M  M      M      H 


^ 

M        t^ao   o 

N  M      M      <N 


-215  0.3 


too 

8^ 
O 

o'd 


i 


M    00 

ON  N 

tot-« 
to^)- 

O^ 
OO 

0    6 


o    o 

u     u     u 


liil 

>    ^°     «-- 


:  S  ;  w>    >  :^°  s«--3 

V  *>*>•£  UU    ^Cuoj-, 

itlllll£alall 


LIBERATION  OF  HEAT  ENERGY. 


17°  C.,  or  64°  F.  In  any  case  where  a  special  temperature 
standard  may  be  used  or  may  have  been  used,  a  column  should 
be  left  for  the  record  of  such  temperature  basis. 

12.  To  exemplify  the  use  of  the  table  and  its  method  of 
compilation  from  the  fundamental  data  on  the  elementary 
gases,  as  given  above,  the  basal  table  herewith  entitled  "  Data 
and  Computations  on  Elementary  Gases  "  may  be  used  as  the 
starting  point.  The  data  are  from  J.  Thompson,  or  other  re- 
liable sources. 

The  atomized  gas  given  as  No.  i  in  the  large  table  is  taken  for 
the  illustration  below.  Column  2,  below,  repeats  the  analysis 
from  the  large  table.  Columns  3  and  4  of  that  table  result  when 
the  values  in  column  2  are  multiplied  by  the  values  in  columns 
10  and  ii  of  the  element  table  preceding.  Column  5  results 
when  the  analysis  figures  in  the  second  column  are  multiplied 
by  the  cubic  foot  requirement  of  that  element  taken  from  col- 
umn 12  of  the  preceding  table.  Totaling  these  constituent  com- 
putations the  total  B.T.U.  and  the  total  cubic  feet  of  air  are 
given;  and  dividing  these  total  B.T.U.'s  by  the  cubic  feet  of 
air  increased  by  one  cubic  foot  of  gas-fuel,  the  results  for  the 
mixture  given  in  columns  14  and  15  of  the  large  table  are 
obtained,  as  in  columns  6  and  7. 

TYPICAL    COMPUTATION   TABLE. 


1 

2 

3 

4 

5 

6 

7 

Constituents  of 
Carbureter  Gas 

Analysis 
or  Volume 
in  Cubic 

B.T.U 

Cubic 

in  100 
Feet. 

Cubic   Feet 
of  Air  per 

Col.  3 
-.-Co\.  5 

Col.  4 
-fCol.  5 

Line   No.  i. 

Feet  in 

Feet  Gas. 

-}-  100. 

+  100. 

100. 

High. 

Low. 

Hydrogen 

5-6 

1853.6 

1560.7 

13-44 

IVlarsh  gas 

CA      Q 

c6od2  3 

51188  8 

^27    O 

Olefiant  gas 

28.9 

46789.1 

43725.7 

4l6.2 

Carbonic  oxide.  . 

8.9 

2933.4 

2933-4 

21.4 

Carbonic  acid.  .  . 

0.9 

Oxygen  

0.21 

Nitrogen  

... 

Totals         

100. 

108518.4 

99408  .  6 

978.04 

100.7 

92.2 

84  THE  GAS-ENGINE. 

30.  Liquid  Fuel.  Petroleum.  —  Another  great  source  ol 
hydrogen  and  carbon  as  fuels  for  industrial  purposes  comes  from 
the  oils  which  are  pumped  up  from  the  earth  or  which  flow  under 
pressure  from  subterranean  reservoirs  and  which  are  desig- 
nated by  the  general  name  of  petroleum.  There  are  oils  of  animal 
origin,  but  they  are  now  supplied  to  such  a  limited  extent  for  fuel 
purposes  as  scarcely  to  deserve  consideration,  and  the  cost  of 
extracting  vegetable  oils  from  the  seeds  or  other  products  which 
carry  them  precludes  the  use  of  such  oils  for  fuel.  Hence  the 
mineral  oil,  or  petroleum,  is  the  principal  source  of  heat  from 
liquids  either  in  its  crude  form  as  it  comes  native  from  the  oil- 
well,  or  after  a  part  of  the  constituents  of  the  natural  oil  have 
been  eliminated  by  the  refining  process.  In  the  present  state  of 
the  art  of  using  liquid  fuel  in  motor-engines,  the  use  of  crude  oil 
is  so  difficult  as  to  be  practically  prohibited.  The  difficulties 
arise  from  the  fact  that  the  mineral  oil  is  not  a  homogeneous 
chemical  substance,  but  is  a  mechanical  mixture  of  several  con- 
stituents having  varying  temperatures  at  which  they  change  their 
state  from  a  liquid  to  a  gas.  The  consequence  of  this  mechanical 
mixture  of  constituents  is  that  the  more  volatile  elements  form  a 
gas  first  and  are  eliminated  from  the  mixture,  leaving  behind  the 
thicker  and  more  viscous  components,  which  presently  form  a 
gum  or  a  solid  mass  in  the  generating  chamber  which  is  difficult  to 
handle.  It  is  much  easier  to  use  the  refined  products  of  the 
refining  process  rather  than  the  crude  oil  in  its  entirety.  The 
average  composition  of  crude  petroleum  is  usually  given  as : 

From  To  Average. 

Carbon '.82  87.1  85 

Hydrogen 11.2  14.8  13 

Oxygen  and  impurities 0.5  5.7  2 

100 


LIBERATION  OF  HEAT  ENERGY. 


Its  specific  gravity  is  from  0.79  to  0.82.  Lima  oil  from  the 
Ohio  wells  is  of  a  dark  green  color,  is  quite  fluid  and  volatile,  and 
has  a  disagreeable  odor.  Its  volatility  makes  it  flame  easily  and 
give  off  an  explosive  vapor  in  a  confined  space.  These  two  prop- 
erties have  resulted  in  restrictions  upon  its  use  in  many  cities;  the 
health  boards  object  to  the  odor,  and  the  fire  departments  to  the 
danger  of  fire  from  explosions.  Hence  the  refining  companies 
have  introduced  what  is  called  fuel-oil.  This  is  the  residue  after 
a  part  of  the  fractional  distillation  process  has  been  completed, 
A  tabular  summary  of  this  process  is  as  follows: 


No. 

Tempera- 
ture Fahr. 
degrees. 

Distillate. 

Prob- 
able Per 
Cent. 

Specific 
Gravity 

Density 
Baume. 

Boiling 
Point 
Fahr. 

Flashing 
Point. 

degrees 

degrees 

i 

2 

H3 
113  to  140 

Rhigolene    J  Petroleum 
Chymogene  j        ether 

traces 

.590  to  .625 

85-80 

104-158 

3 

140  to  158 

Gasolene 

i-5 

.660  to  .670 

•  80-78 

158-176 

4 

1  58  to  248 

Benzine,  naphtha  C 

10.  0 

.680  to  .700 

78-68 

176-21^ 

14 

B 

2-5 

.714  to  .718 

68-64 

212-248 

5 

248  to  347 

"               "        A 

2 

.725  to  .737 

64-60 

248-302 

.32 

Polishing-oils 

6 

338  + 

Kerosene 

50 

•753  to  .864 

56-32 

302-572 

IOO-I22 

7 

482 

Lubricating-  oil 

IS 

.864  to  .960 

32-15 

572  up. 

230 

g 

Paraffine  Wtix 

2 

Residuum  and  loss 

16 

The  distillation  for  fuel-oil  is  stopped  after  the  kerosene  has 
been  obtained.  In  many  refineries  only  the  three  products  of 
crude  naphtha,  burning  oil,  or  kerosene,  and  the  distillate  are 
recognized,  the  latter  being  the  fuel-oil.  Its  average  specific 
gravity  is  about  .818  or  40  Bafume  at  60°  F.,  so  that  a  gallon  weighs 
7.3  pounds,  as  against  6.81  pounds  for  the  crude  oil.  It  flashes 
at  218°  F.,  or  just  above  the  boiling-point  of  water.  It  is  thick  in 
consistency.  The  calorific  power  of  crude  oil  is  from  20,000  to 
21,000  British  thermal  units,  and  that  of  the  fuel-oil  is  from 
17,000  to  19,000  heat-units.  Fuel-oil  is  called  "astatki"  by  the 
Russians.  Thos.  Urquhart  of  Russia,  in  considering  the  use  of 
petroleum  for  locomotives,  gives  the  following  table  of  the  theoreti- 
cal evaporative  power  of  petroleum  in  comparison  with  that  of 
coal,  as  determined  by  Messre.  Favre  and  Silbermann: 


86 


THE   GAS-ENGINE. 


Fuel. 

Specific 
Gravity 
at  32°  F., 
Water  = 

1.  000. 

Chemical  Composition. 

Heating 
Power, 
British 
Thermal 
Units. 

Theoret. 
Evap.,  Lbs. 
Water  per 
Lb.  Fuel 
from  and 
at  212°  F. 

C. 

H. 

0. 

Penna.  heavy  crude  oil  

0.886 
0.884 
0.928 
0.928 

i  .  380 

84.9 
86.3 
86.6 
87.1 

80.0 

13-7 
13.6 
12.3 
11.7 

5-o 

i-4 

O.I 

i  .1 

1.2 

8.0 

20,736 
22,027 
20,183 
19,832 

14,112 

21.48 
22.79 
20.85 

20  -53 
14.61 

Caucasian  light  crude  oil  .  . 
"          heavy  crude  oil  . 
Petroleum  refuse  

Good  English  coal,  mean  of 
98  samples  

The  further  details  of  refining  for  elimination  of  coloring 
matter,  and  the  steps  of  acid  and  alkaline  agitation,  are  aside 
from  the  present  purpose. 

31.  Pintsch   Oil-gas. — The  Pintsch  oil-gas    (Julius   Pintsch, 
Berlin,  1871)  is  a  true  gas  made  in  retorts  by  the  vaporization  of 
crude  petroleum.     From  70  to  85  cubic  feet  of  a  50-  to  6o-candle- 
power  gas  result  from  the  distillation  of  one  gallon  of  oil.     The 
gas  is  rich  in  illuminating  properties  and  does  not  lose  so  much 
of  its  illuminating  power  by  compression  as  a  coal-gas  would. 
This  system  is  much  used  for  the  lighting  of  railway  cars,  but 
air-gas  and  acetylene  systems  compete  with  it.    With  the  air-gas 
system  the  gas  is  heated  before  being  delivered  to  the  burner  by 
passing  through  a  spiral  coil  of  fine  copper  pipe  above  the  lamp 
itself. 

32.  Kerosene.— Kerosene   has    already   been    referred    to    as 
"burning  oil"  or  No  6  in  the  process  of  fractional  distillation  of 
crude  petroleum  (par.  30).     Usually* 3^-  parts  of  crude  oil  render 
one  part  of  kerosene.     The  heat  of  combustion  will  depend  on  the 

-composition,  but  will  range  between  22,000  and  24,000  B.T.U. 
per  pound.  The  quicker  the  distillation  the  poorer  the  product, 
albeit  more  abundant;  but  the  more  abundant  the  lighter  ele- 
ments the  less  safe  is  the  kerosene. 

The  flashing-points  at  which  an  ignitible  vapor  is  given  off 
by  heating  will  range  from  115°  to  125°  F. ;  the  oil  will  itself 
ignite  and  burn  when  heated  to  between  130°  and  140°  F.  This  is 
called  its  burning-point.  It  boils  anywhere  between  the  limits 
of  300°  F.  and  500°  F.,  giving  a  vapor  density  five  times  that  of 


LIBERATION  OF  HEAT  ENERGY.  87 

air,  and  requiring  for  its  combustion  nearly  190  cubic  feet  of  air 
per  pound.  The  principal  component  of  kerosene  in  the  hydro- 
carbon series  is  the  element  decane,  whose  composition  by  the 
formula  CMH2(w+1)  (see  p.  64)  will  be  C10H22.  If  the  kerosene  be 
regarded  as  composed  entirely  of  this  compound,  its  combustion 
will  be  given  by  the  equation 

C10H22  +   020  +  On  -  ioC02+nH20, 


120+22  320+176  440+198 

so  that 

=  3-5P°undsof  oxygen,     or     iff  of  3.5  =  15.21 


pounds  or  15.21X12.387  =  188.4  cubic  feet  of  air  will  be  required 
when  in  its  combustion  it  is  treated  as  a  gas.  Since  the  vapor 
of  kerosene  is  five  times  as  heavy  as  that  of  air,  a  pound  of  vapor 

12.387 
will  occupy  —  -  —  =  2.47  cubic  feet.     The  ratio  of  volumes  will 

therefore  be  —  —  =  76.2  volumes  of  air  to  one  volume  of  kerosene 

vapor.  This  computation  can  be  applied  in  a  later  paragraph 
to  compute  the  temperature  increase  due  to  combustion.  When 
kerosene  is  used  as  a  source  of  heat  for  internal-combustion 
engines  it  is  usually  atomized  or  broken  into  a  mist,  and  is  then 
vaporized  by  heat  so  as  to  form  a  gas.  (See  Chapter  VI,  on 
Kerosene-engines,  and  Chapter  X,  on  Carbureters.)  It  is 
cheaper  than  the  more  usual  gasoline,  but  by  reason  of  the  in- 
conveniences in  starting  up  and  some  easily  superable  difficulties 
in  regulation  du  to  its  variable  composition  it  lias  not  received 
the  attention  which  has  been  given  to  gasoline.  It  does  not 
waste  or  change  its  quality  in  storage;  the  supply  is  practically 
unlimited;  it  is  everywhere  obtainable;  the  fire-  risk  or  insurance 
rate  is  not  increased  by  its  presence.  The  wide  range  of  the 
boiling-point  of  the  commercial  article  has  been  the  source  of 
one  difficulty  in  using  it.  Being  a  mixture  in  any  case,  an 


88  THE  GAS-ENGINE. 

isolated  mass  decomposes  or  " cracks"  6y  heat  into  various 
components,  and  when  heated  too  hot  it  decomposes,  depositing 
its  carbon  in  the  form  of  a  hard  cake  like  coke.  For  the  com- 
plete combustion  of  liquid  kerosene  the  conditions  of  a  lamp- 
wick  are  ideal  by  reason  of  its  presenting  four  essential  conditions  : 

1.  The  heat  for  gasifying  the  oil  is  graduated  from   that  of 
the  containing  vessel  to  the  highest  temperature  of  combustion 
of  the  oil. 

2.  The  combustion  is  slow  enough  to  allow  complete  union 
with  necessary  oxygen  for  combustion. 

3.  With  a  proper  exposure  of  distilling   or  gasifying  surface 
to  the  oxygen,  the  whole  of  the  combustible  is  consumed. 

4.  The  gasification  at  the  flame  is  at  just  the  proper  tem- 
perature, and  the  delivery  of  fuel  is  at  just  the  required  rate. 

If  the  wick  is  turned  too  high,  more  fuel  is  supplied  above 
the  burner  top  than  can  be  gasified  by  the  heat  of  the  flame, 
•and  the  excess  of  carbon  unconsumed  appears  as  a  smoke  with 
a  suffocating  odor.  If  the  wick  is  turned  down,  however,  the 
heat  is  again  too  low  to  consume  the  distilled  gas  and  some  car- 
bonic oxide  is  formed.  Of  course,  if  the  oxygen  supply  is  cut  off 
while  other  conditions  are  retained  normal,  both  of  the  above 
evil  consequences  present  themselves.  In  the  chapter  on  kero- 
sene-engines (Chap.  VI)  some  further  points  will  be  discussed 
concerning  the  conditions  for  its  use  in  motors. 

33.  Gasoline. — Gasoline  is  the  next  higher  or  more  volatile 
distillate  from  crude  petroleum,  having  a  specific  gravity  ranging 
from  the  highest  grade  of  about  88°  Baume  little  used  for  power 
purposes  down  to  68°  B.,  or  with  a  specific-gravity  range  in  the 
ordinary  hydrometer  scale  between  0.680  and  0.710.  The  com- 
mercial names  differ  in  different  places,  but  in  general  the  quali- 
ties and  names  will  be: 

(1)  88°  to  86°  B.  or  .640 light  volatile  oil 

(2)  76°  B.  or  .682 stove-gasoline 

(3)  68°  to  73°  B.  or  .692  to  .709 benzoline 

(4)  62°  B.  or  .730 benzine 


LIBERATION  OF  HEAT  ENERGY.  89 

No.  2  in  the  series  is  the  usual  internal- combustion  motor  fuel, 
but  frequently  this  changes  on  storage  for  any  length  of  time  to 
No.  3,  which  is  sometimes  called  prime  city  naphtha.  Stove- 
gasoline  is  also  locally  known  as  boulevard  gas-fluid.  It  will  be 
observed  from  the  table  in  paragraph  30  that  the  crude  petro- 
leums usually  yieM  but  8  to  10  per  cent  of  gasoline,  so  that  a 
definite  limit  is  set  upon  the  amount  of  it  available  at  any  one 
time.  This  will  have  a  notable  effect  upon  its  price  as  the  use 
of  gasoline  for  fuel  becomes  more  extended  and  the  number  of 
motors  using  it  increases. 

The  boiling-point  of  gasoline  ranges  from  120°  to  250°  Fahr., 
with  an  average  range  between  149°  and  194°  Fahr.  Its  principal 
hydrocarbon  constituents  are  the  elements  hexane  and  heptane 
of  the  series,  which  on  the  formula  CMH2(w+l)  gives  a  composition 
of  C.H14+C7H16.  The  range  is  between  C5H12  and  C7H16.  Tak- 
ing C6Hti  as  the  average  of  all,  the  combustion  computation  will  be 

O12+O7    =   6CO2+7H2O. 


192  +  112  264+126 

This  will  require  -gT  =3.53  pounds  of  oxygen  or  3.  53  X  -  = 

15.3  pounds  of  air  or  189.52  cubic  feet  of  air. 

The  vapor  of  gasoline  is  3.05  times  as  heavy  as  that  of  air. 


Hence  a  pound  of  vapor  will  occupy  —  —   =4.06  cubic  feet  at 

32°  and  one  atmosphere  of  pressure.  Hence  a  pound  of  gasoline 
vapor  occupying  4.06  cubic  feet  will  require  189  cubic  feet  of  air, 
or  the  ratio  of  volumes  of  vapor  to  air  will  be 


This  computation  can  be  later  used  to  compute  the  tempera- 
ture increase.    The  calorific  power  of  gasoline  is  between  18,000 


90  THE   GAS-ENGINE. 

and  20,ooo_  B.T.U.  per  pound  or  690  per  cubic  foot.  Redwood 
found  that  gasoline  vapor  with  air  in  proportions  ranging  between 
5  in  100  up  to  12.5  in  100  were  explosive.  The  mixture  of  n 
per  cent  of  vapor  gave  the  strongest  effect.  Incomplete  com- 
bustion of  gasoline  in  mixtures  results  in  the  formation  of  a 
smoky  mixture  in  the  products,  with  an  offensive  odor.  As  in 
the  case  of  kerosene,  this  phenomenon  results  from  either  too 
much  fuel  in  the  mixture,  or  from  too  little.  The  former  is  the 
more  usual  and  the  more  objectionable. 

The  volatile  elements  in  gasoline  tend  to  escape  from  it  even 
at  ordinary  temperatures,  so  that  the  liquid  alters  and  deteriorates 
in  storage  unless  in  very  tight  metallic  vessels.  The  volatile 
elements  mixing  with  the  air  in  a  vessel  partly  emptied  form  an 
explosive  mixture  which  will  ignite  readily  from  an  open  flame. 
The  heavy  vapor  seeks  the  bottom  levels  in  confined  places 
before  becoming  diffused.  Neither  kerosene  nor  gasolene  acts 
like  water  in  swelling  the  staves  of  wooden  barrels  and  keeping 
such  receptacles  tight  against  leakage  and  loss.  When  gasoline 
is  entrained  by  a  current  of  air,  as  in  a  carburetor  (Chapter  X), 
it  forms  an  air-gas,  or  an  atmosphere  saturated  with  hydrocarbon 
mist.  Gasoline  is  sufficiently  volatile  to  evaporate  completely 
without  additional  heat  when  thus  finely  divided,  and  the  car- 
bureted air  can  be  burned  for  power  or  lighting  purposes.  Much 
car-lighting  by  gas  is  done  on  this  system,  using  compressed  air 
from  the  train-brake  supply.  There  is  no  considerable  storage 
of  gas,  since  such  a  carbureted  atmosphere  is  liable  to  deposit 
its  liquid  hydrocarbon  by  a  sort  of  liquation  in  any  storage  tank 
where  it  may  be  at  rest,  particularly  in  cold  weather.  On  the 
other  hand,  to  pass  this  mixture  through  a  hot  chamber  will  cause 
a  deposit  of  fixed  carbon  or  coke  as  in  the  case  of  kerosene. 

The  arguments  for  gasoline  as  a  fuel  for  motor  vehicles'  are 
the  ease  of  its  vaporization  in  starting  and  running,  in  spite  of 
difficulties  of  maintaining  proper  proportions  of  the  mixture  of 
fuel  and  air  for  varying  conditions  of  load  and  speed. 

34.  Alcohols. — There  are  two  kinds  of  alcohol  used  in  the 


LIBERATION  OF  HEAT  ENERGY.  91 

arts  and  as  sources  of  heat:  methylic  alcohol  or  wood-alcohol, 
which  has  the  chemical  symbol  C2H4O2,  and  ethyl  alcohol,  the 
ordinary  form,  which  is  represented  by  C4H6O2. 

Wood-alcohol  is  formed  by  dry  distillation  of  wood  in  iron 
retorts  (usually  horizontal)  at  a  heat  not  above  900°  F.  It 
has  a  strong  characteristic  odor  and  boils  at  150°  F.  In  the 
United  States  a  considerable  internal-revenue  taxation  is  levied 
upon  alcohol,  which  operates  with  some  hardship  upon  pro- 
ducers of  corn  at  considerable  distances  from  their  market. 
The  transportation  charges  on  the  grain  may  preclude  an 
attractive  profit  upon  the  raw  material,  whereas  in  manufactured 
and  concentrated  form  as  alcohol  the  profit  from  an  acreage 
would  be  a  handsome  one.  The  French  and  German  ministries 
of  agriculture  have  been  encouraging  the  development  of  alcohol- 
motors  with  a  view  of  stimulating  production  of  alcohol-grain 
among  the  farming  districts.  Their  interest  has  developed  a 
process  for  deriving  alcohol  from  the  electrically  manufactured 
carbides. 

Ethyl  alcohol  is  obtained  by  distillation  from  the  fermented 
infusions  of  the  cereal  grains,  which  contain  either  sugar  or  starch. 
It  has  a  specific  gravity  of  0.792  and  boils  at  173°  F.,  but  will 
freeze  only  at  200°  below  zero  when  pure.  It  expands  3^  times 
as  much  as  water  between  32°  and  173°  F. 

Hydrated  alcohols  contain  water  ranging  from  50  per  cent  by 
volume  (proof  spirits)  to  93  per  cent  (cologne  spirits).  The 
affinity  for  water  is  very  strong.  The  table  on  page  91  is  of 
convenient  reference. 

For  the  range  of  percentage  contained  in  that  table  the 
correction  for  temperatures  different  from  60°  F.  should  be 
made  as  follows: 

If  the  density  is  measured  at  a  temperature  above  60°,  0.0005 
should  be  added  to  the  measured  density  for  each  degree  which 
the  temperature  at  the  time  of  the  measurement  differs  from  60°. 
When  the  temperature  at  the  time  of  measurement  is  below 
60°,  the  same  correction  should  be  subtracted  from  the  measured 
density.  The  corrected  density  should  then  be  used  in  the 
table  for  finding  the  true  percentage  of  alcohol. 


92 


THE   GAS-ENGINE. 


SMITHSONIAN  TABLE   OF    SPECIFIC    GRAVITIES    OF 
ETHYL  ALCOHOL. 


•  Specific 
Gravity  at 

Percentage  of  Alcohol. 

Specific 
Gravity  at 

Percentage  of  Alcohol. 

60°  F.  Com- 

60° F.  Com- 

pared  with 

pared  with 

Water  at 

By 

By  Vol- 

Water at 

By 

By  Vol- 

60° F. 

Weight. 

ume. 

60°  F. 

Weight. 

ume. 

0.834       - 

85.8 

90.0 

0.822 

90.4 

93-4 

•833 

86.2 

90-3 

.821 

90.8 

93-7 

.832 

86.6 

90.6 

.820 

91.1 

94.0 

•831 

87.0 

90.9 

.819 

91-5 

94-2 

.830 

87.4 

91.2 

.818 

91.9 

94  -5 

.829 

87.7 

91-5 

.817 

92.2 

94.8 

.828 

88.1 

91.8 

.816 

92.6 

95  -° 

.827 

88.5 

92.1 

•8l5 

93-° 

95-3 

.826 

88.0 

92-3 

.814 

93-3 

95-5 

.825 

89-3 

92.6 

•8l3 

93-7 

95-8 

.824 

89.6 

92.9 

.812 

94.0 

96.0 

.823 

90.0 

93-2 

1 

The  percentage  of  alcohol  found  in  a  sample  is  always  likely 
to  be  greater  when  determined  chemically  than  when  determined 
"by  the  hydrometer,  because  the  presence  of  impurities  in  the 
way  of  solids  dissolved  in  the  alcohol  or  as  any  of  the  series  of 
higher  alcohols  tends  to  make  the  specific  gravity  of  the  sample 
greater,  and  hence  make  it  indicate  too  low  a  percentage  of 
alcohol. 

Pure  alcohol  is  very  inflammable  and  burns  with  a  pale-blue 
smokeless  flame.  Its  calorific  power  is  about  28,500  B.T.U., 
which  runs  down  to  12,000  with  greater  hydration. 

For  motor  purposes  the  custom  has  prevailed  very  widely  to 
mix  the  alcohol  with  some  other  hydrocarbon,  usually  from  the 
petroleum  group.  Such  mixtures  become  undrinkable  and 
are  known  as  "denatured"  alcohol.  For  example,  a  prevalent 
French  mixture  is 

Ethyl  alcohol 100     volumes. 

Methyl    "      .....     10 
Hydrocarbon 0.5      " 


110.5 


LIBERATION  OF  HEAT  ENERGY. 


93 


The  hydrocarbon  is  defined  only  by  its  boiling-boint,  which 
should  be  between  350°  F.  and  440°  F.  It  will  have  a  specific 
gravity  of  .832  to  .835  referred  to  water,  or  about  38°  B.,  and  a 
calorific  power  of  9300  B.T.U.  per  pound.  An  alcohol  mixture 
known  as  electrine  has  a  composition  of  equal  parts  of  the  above 
mixture  with  a  benzol,  resulting  in  a  specific  gravity  of  .835  and 
a  calorific  power  of  13,150. 

A  motor  which  is  to  operate  with  alcohol  in  internal  com- 
bustion should  work  with  a  higher  compression  of  the  charge 
before  igniting  than  is  satisfactory  for  gasoline  or  kerosene.  The 
carbureting  apparatus  has  also  to  be  kept  hotter,  particularly 
if  the  alcohol  is  considerably  hydrated.  Some  tests  by  Delahaye 
with  the  same  motor  gave  the  following  results  in  fuel  consump- 
tion: 


Fuel. 

H.P. 

Pints  per  Hour. 

Pints  per  H.  P. 

6.23 

c  .  i 

0  86 

Carbureted  alcohol   ^o^^ 

6  20 

6    22 

«                  "        "c°7 

6.23 

7  6 

w-yy 

I    22 

6.32 

10.  i; 

I    7O 

An  American  test  with  a  Westinghouse  engine  gave  the 
economy  of  1.2  pints  per  H.P.  per  hour;  Japy  of  Beaucourt  in 
France  reports  1.03  pints  per  H.P.  In  some  results  of  trials  in 
Paris  (1902)  the  thermal  efficiency  of  the  four  fuels  in  motors 
were  given  as: 

For  gasoline 14  to  18  per  cent 

"   kerosene 13  "      " 

"   gas 181031     "      " 

"   alcohol 24  to  28    "      " 

These  results  might  have  been  foreseen  to  some  degree,  since 
the  alcohol  contains  by  weight  a  certain  proportion  of  oxygen, 
which  is  not  a  fuel,  so  that  weight  for  weight  the  gasolines  have 
more  heat  and  power  value  than  alcohols.  The  Delahaye  experi- 
ments give  the  relation  of  gasoline  to  alcohol  to  be  -  —  =  i  .9, 

5-4 

or   the   same   engine   requires    1.9   times    as   much   alcohol    as 
gasoline.     This  has  been  confirmed  by  recent  tests  made  for 


94  THE   GAS-ENGINE. 

the  United  States  Department  of  Agriculture,*  where  the  relation 
of  1.8  was  found,  which  corresponds  so  closely  with  the  relative 
heating  value  as  to  indicate  that  practically  the  thermal  efficiency 
of  the  two  fuels  was  the  same  when  vaporization  is  complete. 
The  advantage  of  alcohol  is  the  fact  of  having  part  of  its  oxygen 
necessary  for  combustion  in  its  own  composition,  so  that  intimate 
mixture  of  fuel  and  oxygen  is  secured  in  part  no  matter  what 
unfavorable  arrangements  may  exist  for  a  proper  mechanical 
admixture.  Alcohol  on  the  other  hand  is  a  very  variable  aggre- 
gate, hydrating  itself  when  exposed  to  damp  air,  so  that  com- 
parisons of  two  alcohol  tests  need  to  be  carefully  made,  lest  the 
two  fuels  of  the  same  name  be  really  quite  different  in  heating 
value.  This  is  true  also  of  the  volatile  gasolines.  Alcohol  is 
particularly  liable  to  partial  vaporization  in  carburetors,  an 
excess  going  through  the  motor  as  a  liquid,  greatly  increasing 
the  apparent  consumption. 

In  comparison  with  gasoline,  alcohol  offers  the  following 
advantages : 

1.  Greater  safety  in  storage,  and  in  its  handling  by  careless 
or   ignorant   persons,    both   ashore   and   afloat.     For   launches 
and  yachts  alcohol  should  supplant  gasoline  for  this  reason. 

2.  The  exhausted  products  of  combustion  and  the  exhaust 
pipe  are  cooler,  diminishing  danger  from  fire,  discomfort  in  the 
engine  room,  and  the  danger  of  burning  the  lubricating  oil. 

3.  The   exhausted   products   are   less   offensive   as   respects 
odor,   and   the   presence   of  smoke.     The   engine   passages   do 
not  clog  with  soot  or  deposits  of  carbon  so  soon,  or  at  all.     Both 
these  difficulties  are  made  less  or  greater  by  the  degree  of  skill 
in  operating,  particularly  if  combustion  is  allowed  to  be  incom- 
plete, or  excesses  of  fuel  and  lubricating  oil  are  permitted. 

On  the  other  hand,  to  secure  equal  thermal  efficiency,  motors 
using  alcohol  should  work  with  a  higher  degree  of  compression 
of  the  mixture  before  ignition.  If  the  maximum  compression 
pressure  with  gasoline  be  taken  at  65  pounds,  with  an  average 
nearer  40  pounds,  the  pressure  with  alcohol  should  be  over  80 

*  "The  Use  of  Alcohol  and  Gasoline  in  Farm  Engines,"  by  C.  E.  Lucke  and 
S-  M.  Woodward,  Government  Printing  Office,  1907. 


LIBERATION  OF  HEAT  ENERGY. 


95 


pounds  per  square  inch;  and  in  engines  to  be  started  by  hand, 
as  in  usual  motor- vehicle  practice,  such  compression  values 
form  an  obstacle  to  change,  or  in  any  use  where  the  cost  of  the 
fuel  is  made  a  secondary  consideration.  This  condition  will 
be  changed  again  should  the  cost  of  petroleum  derivatives,  such 
as  gasoline  and  kerosene,  become  higher  by  the  exhaustion  of 
the  supplies  or  the  increasing  demands  relative  to  the  supply. 
The  sources  for  alcohol  are  practically  inexhaustible  and  are 
self-renewing  under  powerful  natural  law.  The  following 
table  taken  from  the  Bulletin  referred  to  above,  gives  the  estimate 
of  its  authors  as  to  the  relative  quantitative  values  of  these 
considerations : 

COST  OF  ENERGY  IN  FUELS. 


Kind  of  fuel. 

Cost  of  fuel. 

British  thermal  units 
(B.T.U.) 

Number  of 
B.T.U. 
bought 
forli. 

12,500  per  pound  
14,000  per  pound  
550  per  cubic  foot  . 
1,000  per  cubic  foot. 
20,000  per  pound  
20,000  per  pound  
20,000  per  pound.  .  .  . 
20,000  per  pound  
20,000  per  pound  
1  2,000  per  pound  
1  2  ,000  per  pound  

10,000,000 
4,500,000 
550,000 
10,000,000 
3,650,000 
1,200,000 
400,000 
i  ,200,000 
400,000 
270,000 
200,000 

Large  anthracite  

i.  oo  per  1,000  cubic  feet 
.10  per  1,000  cubic  feet 
.04  per  gallon  
.10  per  gallon  
.30  per  gallon  
.10  per  gallon  

Natural  gas  

Crude  oil 

Kerosene  

Do 

Do. 

.30  per  gallon  

Do. 

FUEL  COST  OF  POWER. 


Fuel  and  type  of  Plant. 

Fuel  required 
per  horse- 
power per 
hour. 

British 
thermal 
units  re- 
quired per 
horse-power 
hour. 

Thermal 

efficien- 
cy. 

Cost  of  fuel. 

Cost  of 
fuel  per 
horse- 
power 
per  hour. 

Anthracite  coal  : 
Large  steam  plant    . 

2  pounds. 

25,000 

Per  cent 
10 

$2.50  per  ton  

Cents. 

O.2? 

Do.....  

2  pounds 

Small  steam  plant.  . 

7  pounds. 

100,000 

2k 

2.50  per  ton  

Do....    

7  pounds. 

3 

6  25  per  ton 

Producer  gas  plant  . 

impounds 

14,000 

18 

2.50  per  ton    .  .             ... 

DO.  ..;..., 

ii  pounds 

18 

Do  

2  pounds  

25,000 

10 

2.50  per  ton  

Do  

2  pounds  

25,000 

10 

6.25  per  ton  

•57 

Illuminating  gas  
Crude  oil  

24  cubic  feet. 
1.4  pints  

12,000 

20 

i  .00  per  i  ,000  cubic  feet 
04  per  gallon 

2.  2O 

.68 

Gasoline  

i  .  i  pints  

13,400 

10 

.15  per  gallon  r  .  . 

1.70 

Do... 
Alcohol.  

i.i  pints  

13.400 

19 

.30  per  gallon  

3-40 

Do  

rtlQ 

•70 

0  Efficiency  of  alcohol  is  assumed  to  be  the  same  as  that  of  gasoline  for  identical  conditions  of 


96  THE  GAS-ENGINE. 

The  United  States  government  by  enactments  of  its  Federal 
Congress  in  1905-1906  removed  part  of  the  restrictive  revenue 
exactions  from  alcohol  to  be  used  in  industry,  keeping,  however, 
the  procedure  for  its  manufacture,  storage  and  distribution 
under  close  official  surveillance  and  control,  and  compelling  its 
denaturization  to  be  perfect  and  satisfactory  to  designated 
inspectors,  and  to  be  done  by  them.  This  step  will  doubtless 
lead  to  a  wider  use  of  denatured  alcohol.  Their  requirement 
by  law  is  that  to  100  volumes  of  ethyl  or  grain  alcohol  of  a 
strength  not  less  than  90  per  cent  there  must  be  added  either 
10  volumes  of  methyl  or  wood  alcohol  and  one-half  of  one 
volume  of  benzine;  or  2  volumes  of  methyl  alcohol  and  one  half 
of  one  volume  of  pyridin  bases.  A  proof  gallon  in  the  United 
States  contains  50  per  cent  of  alcohol  by  volume  and  the  bal- 
ance is  water.  In  Germany  the  strength  is  stated  in  percentage 
by  weight.  A  technical  commission  appointed  under  the  above 
act  made  very  thorough  experiments,  and  reported  in  the  Bul- 
letin above  referred  to  as  follows : 

(a)  Any  engine  on  the  American  market  in  1907  operating 
with  kerosene  or  gasoline  can  operate  with  alcohol  fuel  with- 
out any  structural  change  whatever,  with  proper  manipu- 
lation. 

A  fair  average  or  approximate  relation  for  the  three  fuels  to 
each  other  would  give: 


Fuel. 

Specific 
Gravity. 

Pounds  per 
Gallon. 

Gasoline 

0.71 

tr.n 

Kerosene 

O   80 

6    7 

o  ?  per  cent 

grain  alcohol       ..... 

0    82 

6.8 

oo  per  cent 

grain  alcohol    

0.8^ 

6.0 

(6)  It  requires  no  more  skill  to  operate  an  alcohol  engine 
than  one  intended  for  kerosene  or  gasoline. 

(c)  There  is  no  reason  to  suppose  that  the  cost  of  repairs  and 
lubrication  will  be  any  greater  for  an  alcohol  engine  than  for 
one  built  for  kerosene  or  gasoline. 


LIBERATION  OF  HEAT  ENERGY.  97 

(d)  The  different  designs  of  gasoline  or  kerosene  engines  are 
not  equally  well  -adapted  to  the  burning  of  alcohol,  though  all 
may  burn  it  with  a  fair  degree  of  success. 

(e}  The  thermal  efficiency  of  such  engines  can  be  improved 
when  they  are  to  be  operated  with  alcohol  by  altering  the  con- 
struction and  functioning  of  the  carburetor  so  as  to  give  complete 
vaporization,  and  particularly  in  cold  weather;  and  secondly  by 
increasing  the  compression  very  materially. 

(/)  An  engine  designed  for  gasoline  or  kerosene,  without 
any  material  alterations  to  adapt  it  to  alcohol,  gives  about  10  per 
cent  more  power  than  when  operated  with  gasoline  or  kerosene, 
but  at  the  expense  of  greater  consumption  of  fuel.  This  increase 
can  be  raised  to  20  per  cent  by  alterations  adapting  the  engine 
to  the  new  fuel. 

(g)  Because  of  this  increased  output  of  power  without  cor- 
responding increase  in  size,  alcohol  engines  should  sell  for  less 
per  horse-power  capacity  than  gasoline  or  kerosene  engines  of 
the  same  class.  Until  the  interest  of  builders  is  drawn  to 
this  phase  of  the  industry  by  action  of  buyers  this  will  not  take 
place. 

(h)  Alcohol  may  immediately  compete  with  gasoline  as  a 
fuel  for  engines  in  localities  where  the  supply  of  cheap  raw 
material  for  manufacture  of  denatured  alcohol  exists,  which  are 
at  the  same  time  remote  from  the  sources  of  supply  of  gasoline. 

(i)  In  most  localities  it  is  unlikely  that  alcohol  power  will  be 
cheaper  than  gasoline  for  some  time  to  come. 

An  objection  which  has  revealed  itself  with  motors  using 
alcohol  is  the  excess  of  water-vapor  formed  in  the  cylinders,  and 
that  this  water- vapor,  absorbing  the  acetic  acid  which  forms  with 
the  occasional  incomplete  combustion  of  the  alcohol,  attacks 
and  corrodes  metal  surfaces  and  scores  valves  and  seats.  Proper 
manipulation  reduces  this  to  an  inconsiderable  difficulty. 

35.  Products  of  Combustion  of  a  Gas. — In  the  discussion  of  par. 
1 1  it  was  made  apparent  that  the  combustion  of  carbon  and  hydro- 
gen gave  the  weight  of  the  products  resulting  from  such  combustion. 
It  will  be  apparent  that  when  the  volume  is  to  be  considered 


98  THE  GAS-ENGINE. 

this  will  vary  with  the  temperature  of  such  products  of  combustion. 
Anticipating,  for  the  moment,  a  later  discussion  which  will  define 
the  term  "absolute  temperature"  it  may  be  said  here  that  if  F0 
denote  the  volume  at  the  temperature  of  melting  ice,  and  T0  the 
corresponding  absolute  temperature,  while  V  and  T  are  the 
volume  and  absolute  temperature  corresponding  to  the  state  of 
the  hot  and  expanded  gases,  the  volumes  will  be  proportional  to 
these  absolute  temperatures,  whence 


U          ((       It         ((  (I 

(I       (I     It      It  (t 


rp       . 

*  0 

Similarly  if  the  initial  volumes  be  observed  or  taken  at  62°  F., 
the  final  or  expanded  volumes  can  be  calculated.     For  example, 

CO2    at  62°  occupies     8  .  594  cu.  ft.  to  the  pound; 

TT  tt     a  a  T/~in  ll      l(    lt      ll          il 

S02     "    "        "  5.848 

N        "    "        "         13.501 

whence         .03660x8.594=    .3150     =cu.  ft.  of  CO2  at  62°; 
.o9oH  Xi9o    =i.9H        =  "   "    "H      "    " 
.28        X5.85  -    .1178     =  "   "    "SO2   "    " 

.08590)  N  (i.i6C  )  __  a    <<  «N       «    « 

.2584Hr  '   (3-49H{  ' 

Adding  and  neglecting  the  smaller  weight  of  SO2,  the  volume 
at  62°  F.  becomes 


and  the  volume  V2  at   any  greater   temperature  will   be   found 

T 
by  multiplying  the  above  expression  by  the  fraction  ~,  in  which 

7\  is  the  absolute  temperature  corresponding  to  62°  F.,  and  T2 
the  absolute  temperature  at  which  the  volume  is  sought. 

36.  The  Dilution  of  the  Mixture.  —  The  discussion  in  para- 
graphs 1  1  and  1  2  made  it  apparent  that  for  complete  combustion 
of  hydrogen  and  carbon  in  air  a  certain  minimum  weight  or 
volume  was  required  in  order  to  supply  the  necessary  quantity 


LIBERATION  OF  HEAT  ENERGY.  99 

of  oxygen  for  that  combustion.  Experience  has  shown  that  in 
the  combustion  of  solid  fuels  under  constant  pressure  in  air,  the 
distillation  process  preceding  the  true  combustion,  a  certain  excess 
of  air  is  desirable  above  that  required  for  chemical  combination. 
This  will  be  often  one  and  a  half  times  or  even  as  much  as  twice 
the  theoretical  or  computed  amount  from  the  combining  weights. 
In  gas  combustions,  however,  either  in  fires  or  in  the  cylinders  of 
engines,  this  dilution  process  is  not  required  to  the  same  extent, 
and  is  prejudicial  to  the  production  of  high  temperatures.  In 
the  slow  process  of  distillation-combustion  of  solids  the  products 
of  combustion  are  not  supporters  of  combustion,  but  the  latter 
must  be  deported  in  a  current  of  excess  of  air  in  order  to  bring 
necessary  additional  oxygen  to  reach  the  burning  surfaces.  With 
gaseous  combustions,  and  particularly  when  so  mixed  as  to  be 
self-propagating,  the  flame  will  carry  through  the  mass  of  gas 
without  action  from  the  burnt  gases  present.  Hence  an  excess  of 
air  merely  means  an  increase  in  the  denominator  of  the  second 
member  of  the  equation. 

T  -T  =      yQ 

(oc+y)C> 

in  par.  20,  whereby  the  rise  in  temperature  due  to  yQ  will  be 
diminished.  The  unnecessary  weight  of  air  and  its  inert  nitrogen 
has  to  be  heated  by  the  expenditure  of  the  fuel  energy,  and  for  a 
given,  amount  of  such  energy  the  less  the  mass  to  be  heated  the 
hotter  it  will  be. 

On  the  other  hand,  upon  the  economic  side,  for  a  given  volume 
of  engine- cylinder,  it  will  be  cheaper  to  fill  the  latter  with  as  lean 
a  mixture  of  gas  and  air  as  is  consistent  with  positive  ignition  of 
the  charge,  since  the  gas  is  the  element  which  costs  and  the  air  is 
free.  When  an  excess  of  air  is  used  above  what  the  gas  needs 
for  combustion,  there  will  be  oxygen  found  in  the  products  of 
combustion  other  than  that  in  combination  with  the  carbon  as 
CO2.  Hence  it  becomes  a  matter  of  great  importance  to  mix  the 
proportions  of  fuel  and  air  for  the  gas-engine,  with  a  given  com- 
pression pressure,  so  as  to  avoid  incomplete  combustion  on  the 


100 


THE   G4S-ENGINES. 


one  hand,  with  its  deposit  of  soot  or  lampblack  in  the  cylinder 
and  passages,  and  the  offensive  odor  of  the  exhaust;  and  on  the 
other  the  use  of  excess  of  fuel  entailing  waste  and  unnecessary 
cost,  and  diminishing  the  effective  power  of  the  motor.  If  the 
compression  pressure  can  be  increased  with  safety,  then  a  more 
dilute  mixture  can  be  made  to  give  the  same  card  area  and  the 
same  .mean  effective  pressure.  Some  interesting  and  useful 
experiments  with  a  gas  whose  analysis  showed  a  requirement 
of  5  or  5.5  volumes  of  air  to  i  of  gas  in  an  apparatus  to  be  described 
in  Chapter  XIX  gave  results  which  are  shown  graphically  in  Fig. 
12.  The  points  on  the  horizontal  line  indicate  the  mixtures  of 
gas  and  air,  and  the  vertical  ordinates  the  pressures  caused  by 
igniting  such  mixtures.  The  highest  pressures  belong  to  the 
correct  proportions,  but  the  engine  would  operate  all  right  with 
nearly  twice  as  much  fuel  as  was  necessary,  and  such  extravagant 
working  might  go  undetected  for  some  time.  At  the  other  end 
of  the  series,  the  danger  appears  of  a  mixture  so  poor 
in  fuel  elements  that  it  will  ignite  with  difficulty  or  not 
at  all.  It  will  be  shown  in  Chapter  XIX  that  excess  of 
products  of  combustion  may  so  dilute  a  mixture  as  to  produce 
the  same  effect,  but  this  excessive  dilution  will  not  be  normal  in 
the  internal-combustion  motor.  The  tests  in  this  same  chapter  will 
show  why  the  relations  of  gas  to  air  of  i :  12  or  i :  13  for  rich  gas 


100- - 


1  3 


have  been  chosen.  The  student  is  referred  to  further  considera- 
tion of  these  questions  under  the  heads  of  ignition,  carburation, 
governing,  and  manipulation,  in  their  respective  chapters.  The 


LIBERATION  OF  HEAT  ENERGY. 


101 


75 


experienced  operator  of  an  internal-combustion  motor  will  have 
observed  the  effect  of  stronger  propelling  pressures  as  he  in- 
creases the  ratio  of  air  to  gas,  but  will  also 
have  noted  the  approach  to  the  limit  where 
the  charge  of  mixture  does  not  always  ignite 
under  these  conditions. 

37.  Gas  Analysis.  Elliot's  Gas  Appa- 
ratus.— It  will  be  aside  from  the  present 
purpose  to  go  at  all  exhaustively  into  the 
problem  of  gas  analysis,  or  that  of  the 
products  of  combustion.  As  some  general 
knowledge  may  be  useful,  however,  the 
Elliot  apparatus  and  the  Orsat  are  illustrated 
for  their  respective  uses.  Fig.  13  shows  the 
Elliot  apparatus.  The  constituents  for  whose 
determination  it  is  adapted  are  CO2,  CO,  O, 
H,  N,  CH4,  and  illuminants.  The  candle- 
power  of  a  water-gas  is  about  twice  the 
percentage  of  illuminants  in  it;  with  a  coal- 
gas  the  multiplier  is  about  3.5. 

The  three  glass  tubes  in  the  apparatus 
may  be  called  the  laboratory-  or  reagent- 
tube,  on  the  right,  surmounted  by  the  funnel 
for  the  introduction  of  the  absorbent  liquid; 
the  measuring-tube,  on  the  left,  for  measuring 
after  each  reaction  the  volume  of  gas  not 
acted  on  by  the  test;  and  the  explosion-tube. 

The  usual  quantity  in  a  test  is  100  cubic 
centimetres.  The  CO2  is  determined  by  FIG.  13. 

introducing  the  measured  volume  from  the 
measuring-tube  into  the  laboratory-tube,  and  introducing 
through  the  funnel  5  cubic  centimetres  of  strong  potassic 
hydrate  (KOH).  The  gas  transferred  back  to  the  measuring- 
tube  shows  by  a  diminished  volume  the  amount  of  CO2 
which  it  has  lost.  For  the  illuminants  a  few  drops  of 


102  THE  GAS-ENGINE. 

bromine  in  water  are  allowed  to  enter  the  laboratory-tube 
after  the  gas  has  been  transferred  back  to  it  from  the  measur- 
ing-tube. The  tube  fills  with  red  fumes  which  are  absorbed 
by  a  second  introduction  of  potassic  hydrate.  The  gas  when 
back  into  the  measuring-tube  will  show  a  second  reduction 
in  volume.  For  oxygen  a  strong  KOH  solution  is  mixed 
with  pyrogallic  acid.  For  CO  a  saturated  solution  of  cuprous 
chloride  in  strong  HC1  is  used.  For  hydrogen  and  marsh- 
gas  the  explosion-tube  is  used.  The  volume  of  the  sample 
is  mixed  with  twice  its  volume  of  oxygen  and  an  equal 
volume  of  atmospheric  air,  and  the  mixture  fired  by  the 
electric  spark.  The  CO 2  formed  by  the  explosion  is  absorbed 
by  KOH  as  in  the  first  step,  and  the  hydrogen  which  formed 
water  goes  out  with  the  displacing  liquids.  When  the  gas 
is  cool,  measure  what  remains  in  the  measuring-tube,  and  it 
may  be  called  nitrogen  to  make  up  the  full  one  hundred  per 
cent.  The  above  treatment  has  not  referred  to  detail  nor  pre- 
cautions, and  has  not  elaborated  the  computations  by  formula 
to  determine  the  proportions  of  CH4  and  H  resulting  from  noting 
the  proportionate  contraction  of  volume  after  explosion. 

The  interest  attaching  to  such  analysis  as  the  foregoing  to 
the  student  of  the  power  problem  is  the  relation  which  the  com- 
position of  the  gas  bears  to  its  computed  or  theoretical  calorific 
power,  or  to  the  actual  calorific  power  as  observed  in  calorimeters. 

38.  Analysis  of  Products  of  Combustion.  Orsat's  Apparatus. 
— It  is  often  convenient,  also,  to  make  a  similar  analysis  of  the 
products  of  combustion,  in  order  to  make  sure  that  the  com- 
bustion has  been  complete  and  the,  mixture  wisely  selected.  An 
excess  of  oxygen  would  not  only  make  the  mixture  difficult  to 
ignite,  but  it  would  lower  the  temperature  on  ignition,  and  any 
considerable  quantity  of  carbonic  oxide  in  the  products  of  com- 
bustion would  not  only  mean  a  waste  of  carbon,  but  would  indi- 
cate the  danger  of  explosions  in  the  exhaust  pipe  or  passages, 
which  are  inconvenient  and  possibly  dangerous.  The  apparatus 
which  is  most  used  in  analyzing  the  products  of  combustion  is 


LIBERATION  OF  HEAT  ENERGY. 


103 


known  as  the  Orsat  apparatus  and  is  illustrated  in  Fig.  14.  P'", 
P",  and  P'  are  pipettes  containing,  respectively,  solution  of  caustic 
potash  to  absorb  carbon  dioxide,  pyrogallic  acid  and  caustic 
potash  to  absorb  oxygen  and  cuprous  chloride  in  hydrochloric 
acid  to  absorb  carbon  monoxide. 

At  d  is  a  cock  to  control  the  admission  of  gas  to  the  apparatus; 
at  B  is  a  graduated  burette  for  measuring  the  volumes  of  gas; 
and  at  A  is  a  pressure-bottle  connected  with  B  by  a  rubber  tube 


FIG.  14. 

- 

to  control  the  gases  to  be  analyzed.  The  pressure-bottle  is 
commonly  filled  with  water,  but  glycerine  or  some  other  fluid 
may  be  used  when,  in  addition  to  the  gases  named,  a  determina- 
tion of  the  moisture  or  steam  in  the  flue-gases  is  made. 

The  several  pipettes  P',  P",  and  P1"  are  filled  to  the  marks 
g,  /,  and  e  with  the  proper  reagents,  by  aid  of  the  pressure-bottle  A . 
With  a  three-way  cock  to  open  to  the  atmosphere,  the  pressure- 
bottle  A  is  raised  till  the  burette  B  is  filled  with  water  to  the  mark 


THE  GAS-ENGINE. 

m\  communication  is  then  made  with  the  flue,  and  by  lowering 
the  pressure-bottle  the  burette  is  filled  with  the  gas  to  be  analyzed, 
and  two  minutes  are  allowed  for  the  burette  to  drain.  The  pressure- 
bottle  is  now  raised  till  the  water  in  the  burette  reaches  the  zero 
mark  arid  the  clamp  c  is  closed.  The  valve  in  the  pipe  to  the 
flue  is  now  opened  momentarily  to  the  atmosphere  to  relieve 
the  pressure  in  the  burette.  Now  open  the  clamp  c  and  bring 
the  level  of  the  water  in  the  pressure-bottle  to  the  level  of  the 
water  in  the  burette,  and  take  a  reading  of  the  volume  of  the  gas 
to  be  analyzed ;  all  readings  of  volume  are  to  be  taken  in  a  similar 
way.  Open  the  cock  g  and  force  the  gas  into  the  pipette  P"f 
by  raising  the  pressure-bottle,  so  that  the  water  in  the  burette 
comes  to  the  mark  m.  Allow  three  minutes  for  absorption  of 
carbon  dioxide  by  the  caustic  potash  in  P'n ',  and  finally  bring 
the  reagent  to  the  mark  a  again.  In  this  last  operation,  brought 
about  by  lowering  the  pressure-bottle,  care  should  be  taken  not 
to  suck  the  caustic  reagent  into  the  stop-cock.  The  gas  is  again 
measured  in  the  burette,  and  the  diminution  of  volume  is  recorded 
as  the  volume  of  carbon  dioxide  in  the  given  volume  of  gas.  In 
like  manner  the  gas  is  passed  into  the  pipette  P",  where  the 
oxygen  is  absorbed  by  the  pyrogallic  acid  and  caustic  potash; 
but  as  the  absorption  is  less  rapid  than  was  the  case  with  the 
carbon  dioxide,  more  time  must  be  allowed,  and  it  is  advisable 
to  pass  the  gas  back  and  forth,  in  and  out  of  the  pipette,  several 
times.  The  loss  of  volume  is  recorded  as  the  volume  of  oxygen. 
Finally,  the  gas  is  passed  into  the  pipette  P',  where  the  carbon 
monoxide  is  absorbed  by  cuprous  chloride  in  hydrochloric  acid. 
The  solutions  used  in  the  Orsat  apparatus  are: 

P'".    Caustic  potash,  i  part;  water,  2  parts. 
P".     Pyrogallic  acid,  i  gram  to  25  cc.  of  caustic  potash. 
P1 '.     Saturated  solution  of  cuprous  chloride  in  hydrochloric 
acid  having  a  specific  gravity  of  i.io. 

These  reagents  will  absorb  per  cubic  centimetre: 


LIBERATION  OF  HEAT  ENERGY.  1036 

P"f .  Caustic  potash  absorbs  40  c.c.  of  CCb; 

P".    Pyrogallic  of  potash  absorbs  22    "     "  oxygen; 
P'.     Cuprous  chloride  absorbs         6    "     "  CO. 

Improvements  in  the  Orsat  apparatus  and  its  manipulation 
have  been  made  by  Hempel,  Carpenter,  Hale,  and  others,  and 
the  student  is  referred  to  Hempel' s  treatise  for  further  detail. 


CHAPTER  III. 

THE  MECHANICAL  ENERGY  FROM  EXPANSION  OF   GAS 
AND   AIR. 

39.  Introductory.     Mechanical    Equivalent    of    Heat. — The 

unit  of  work  for  industrial  purposes  is  the  foot-pound.  It  means 
the  amount  of  energy  required  or  developed  when  one  pound 
moves  through  a  space  of  one  foot  in  one  unit  of  time,  which  is 
usually  the  second.  It  was  found  by  James  Watt,  as  the  result 
of  experiment,  that  the  average  high-powered  draught-horse 
could  do  an  amount  of  work  in  foot-pounds  which  was  repre- 
sented by  the  product  of  330  pounds  into  100  feet  per  minute 
so  that  33,000  foot-pounds  became  established  as  the  horse-power 
per  minute 

It  was  ascertained  by  the  physicist  Joule,  as  corrected  by 
later  determinations,  that  the  amount  of  heat  necessary  to  raise 
one  pound  of  water  i°  F.  was  equivalent  to  the  mechanical  energy 
represented  by  778  foot-pounds,  and  that  the  quantity  of  heat  to 
raise  a  unit  weight  of  water  i°  was  always  convertible  quantita- 
tively into  foot-pounds,  and  vice  versa. 

The  quantity  of  heat  was  designated  as  a  heat-unit,  and  the 
equivalent  in  foot-pounds  has  been  designated  as  the  mechanical 
equivalent  of  heat. 

In  countries  using  the  metric  system  of  weights  and  measures 
the  unit  of  force  is  the  kilogram,  and  the  unit  of  path  is  the  metre. 
The  product  of  effort  multiplied  by  its  path  is  called  a  kilogram- 
metre  in  these  units.  The  following  table  shows  the  relations  of 

the  three  most  usual  values  for  the  horse-power: 

104 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


105- 


Horse-power. 

English 
Foot-pounds 
per  Minute. 

French 
Kilogrammetres 
per  Minute. 

Austrian 
Foot-pounds 
per  Minute. 

English  and  American  .... 

33.OOO 

4,?72   O 

2C.774. 

French                                      .  . 

32,470.4 

4,^OO 

2^,^6r    * 

Austrian  

33,034.  2 

4,^40.  S 

2^,800 

Convenient  transformations  of  the  British  and  metric  heat- 
unit  values  are  given  in  the  following: 

A  French  Calorie  =  i  kilogram  of  H2O  heated  i°  C.  at  or 
near  4°  C. 

A  British  Thermal  Unit  (B.T.U.)  =  i  Ib.  of  H2O  heated  i°  F. 
at  or  near  39°  F. 


A  Pound-calorie  Unit 


i  Ib.  of  H2O  heated  i°  C.  at  or  near 


4°C. 

i  French  Calorie  =  3.968  B.T.U.  =  2.2046  pound-calories. 

i  British  Thermal  Unit  =  .252  French  calories  =  .555  pound- 
calories. 

i  calorie  per  cubic  meter  =  0.113  B.T.U.  per  cubic  foot. 

i  B.T.U.  per  cubic  foot  =  8.91  calories  per  cubic  metre. 

i    Pound-calorie  =  1.8   B.T.U.  =  .45   French  calories. 

i  B.T.U.  =  778  ft.-lbs.  =  Joule's  mechanical  equivalent  of 
heat. 

i  H.P.  =  33,000  ft.-lbs.  per  minute. 

=  *f?JA  =  42.42  B.T.U.  per  minute. 
=    42.42  X  60  =  2545  B.T.U.  per  hour. 

40.  The  Piston-motor.  Mean  Effective  Pressure.  —  The  only 
continuous  motion  in  industry  is  the  rotary  motion.  The  most 
convenient  form  for  utilizing  pressure  to  produce  continuous 
rotary  motion  is  to  have  a  piston  travel  back  and  forth  in  a 
cylinder  and  transform  its  reciprocating  motion  by  means  of  a 
crank  and  connecting-rod  into  such  continuous  rotary  motion. 
In  motors  of  this  class,  which  will  be  called  piston- motors,  the 
work  done  in  the  cylinder  per  minute  will  be  the  product  of  the 
pressure  upon  the  piston  in  pounds  multiplied  by  its  travel  in 
feet.  That  is,  if  the  pressure,  constant  or  variable,  upon  the 


106  THE  GAS-ENGINE. 

head  of  the  piston  be  denoted  by  P  in  pounds  per  square  inch 
and  the  area  in  square  inches  be  denoted  by  A,  the  product  PA 
will  be  the  total  effort  in  pounds  pushing  or  pulling  that  piston. 
If  the  stroke  of  the  piston  in  the  cylinder  be  designated  in  feet 
by  L,  and  the  number  of  times  that  the  piston  makes  this  trav- 
erse by  N,  it  will  be  apparent  that  the 

Work  per  minute  =  PA  X  LN. 

If  both  members  of  this  equation  be  divided  by  33,000,  the  first 
member  becomes  horse-power  and  the  expression  reads: 

H  p   =  PA  X  LN. 

33.000 

In  the  gas-engine,  N  will  not  be  the  number  of  traverses 
which  the  piston  makes  per  minute,  but  will  be  the  number  made 
under  the  effort  of  the  working  medium.  If  the  engine  is  single- 
acting  and  operates  through  the  Otto  cycle  (par.  62),  N  will  be 
the  number  of  explosions  or  ignitions  per  minute. 

If  this  pressure  denoted  by  P  is  constant  and  uniform  through- 
out the  stroke,  the  expression  needs  no  correction  or  revision. 
If  that  pressure,  however,  is  a  variable,  then  it  is  apparent  that 
P  must  be  the  mean  of  the  varying  pressures  throughout  the 
length  of  the  stroke,  and  the  value  of  that  mean  pressure  must 
be  found  either  by  observation  with  proper  instruments  or  by 
calculation. 

If  the  area  A  in  the  foregoing  equation  be  expressed  in  square 
feet,  and  L  in  linear  feet,  the  product  AL  becomes  the  volume  of 
the  cylinder  in  cubic  feet  and  can  be  designated  by  V.  If  AT  be 
one  traverse  and  the  pressure  P  be  expressed  in  pounds  per 
square  foot,  we  have  the  expression 

Work  per  stroke  =  PV. 

This  equation  is  the  general  form  used  by  physicists  in  their 
formula  and  discussions.  F  is  the  final  volume  filled  by  the 
medium  as  the  piston  makes  its  traverse  from  initial  to  final 
position  in  the  stroke;  if  it  be  the  volume  filled  by  one  pound 
of  the  medium  used,  it  denotes  the  work  of  such  unit  weight  of 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


107 


medium  acting  under  the  mean  effective  pressure  throughout 
that  stroke. 

In  the  gas-engine,  however,  by  reason  of  the  directness  of  the 
transfer  of  heat  energy  into  work  in  the  cycle  of  the  cylinder 
working,  an  expression  of  the  same  truth  in  a  more  detailed 
form  leads  to  some  very  practical  results.  If  the  volume  of  gas 
mixture  filling  the  cylinder  volume  at  atmospheric  pressure  at 
the  end  of  the  stroke  which  has  drawn  it  in  be  called  the  initial 
volume,  and  be  denoted  by  Ft,  and  the  volume  after  the  com- 
pression is  complete  be  called  its  final  volume  and  be  denoted  by 
F/,  then  the  piston-displacement  per  stroke  will  be 

Piston- displacement  =  Vt  —  F/, 
and  the  work  per  stroke  as  above 

W  =  [M.E.P.]  X  (Vi  -  F,). 

But  it  is  also  true,  and  will  be  further  discussed  for  quantitative 
results  in  paragraph  47,  that  the  efficiency  of  a  conversion  of 
heat  into  work  is  measured  by  the  relation  of  output  to  input, 
or  the  ratio  of  work  done  in  foot-pounds  to  heat  energy  supplied 
in  heat  units;  or,  W  =  778  QE  since, 

_  ~  .  ,.,       Work  done  in  foot-pounds 

Efficiency  =  E  =  .   r — - — . 

Heat  supplied  in  units 

But  the  computations  for  the  data  in  columns  15  and  16  of  the 
large  table  in  paragraph  29  made  it  clear  what  heat  energy  Q 
could  be  drawn  into  the  cylinder  per  cubic  foot  in  the  mixture 
of  gas  and  air  so  proportioned  as  to  burn  completely;  hence  the 
quantity  (F<  —  F/)  in  cubic  feet,  when  multiplied  by  778  should 
give  the  total  work  units  capable  of  being  supplied  in  one  stroke ; 
whence  the  work  done  should  equal  both 

Work  done  =  Q  X  E,  X  778; 
and  Work  done  =  (M.E.P.)  (7,  -  Vf). 

Whence,  equating,  and  changing  the  latter  into  pounds  per 
square  inch  for  convenient  comparison, 

778  QE  5.4  Q       x  E 

144  (V<  -  F,)  -  (F,  -  F,)  ' 
This  enables  columns  15  and  16  of  paragraph  29  to  be  used  to 


io8  THE  GAS-ENGINE. 

find  the  M.E.P.  with  any  fuel  whose  analysis  is  known  or 
assumed,  when  E  also  is  computed  as  in  paragraph  47,  where  it 
will  be  shown  to  be  a  function  of  the  compression  pressures 
admissible  with  that  fuel.  The  reader  is  referred  to  that  section 
for  quantitative  values  for  this  factor.  If  (F,-  —  F/)  be  one 

cubic  foot  then-^r  =  B.T.U.  per  cubic  foot  of  the  mixture  of 
gas  and  air,  and  the  quantity  in  the  table  in  paragraph  29  may 

TT 

be  used  directly  in  the  form  of  -  — ,  giving  in  pounds  per  square 
inch, 


as  therein  discussed.     (See  also  par.  200.) 

An  effort  has  been  much  in  evidence  recently  to  simplify  the 
horse-power  for  the  gas-engine,  by  reducing  the  variable  factors 
which  are  nearly  uniform  for  most  motors  of  the  same  class  into 
one  factor  which  is  assumed  constant  for  the  time  and  to  apply 
to  all  engines  of  its  class  and  type.  The  errors  of  this  are  plainly 
due  to 

1.  Neglecting  the  variation  in  the  value  of  E  with  different 
compressions. 

2.  Assuming  that  Q  or  its  derivative  H  are  the  same  for  all 
fuels. 

3.  Assuming  all   motors   to   have   practically  the  same  ratio 
between  their  net  or  brake  horse-power  at  the  shaft,  and  the 
effort  in  foot-pounds  upon  the  piston  head,  or  that  all  engines 
have  the  same  mechanical  efficiency. 

4.  Assuming  that  all  motors  attain  the  same  possible  maxi- 
mum efficiency  due  to  their  design  because  there  are  no  leakages 
or  poor  adjustments  or  other  defects  tending  to  lower  the  output 
of  power. 

An  example  of  such  a  formula  has  the  form: 

nd2LN 

Brake  horse- power  =  — — — , 

K. 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  109 

in  which  d  is  the  cylinder  diameter,  in  inches,  L  the  length  in 
inches  (or  feet),  n  the  number  of  cylinders,  and  K  carries  in  it 
the  constants  33,000  and  TT  and  an  assumption  of  the  mean 
pressure.  For  engines  of  a  special  class,  as  in  motor  cars,  the 
apparent  simplification  may  be  carried  further,  as  in  a  recent 
motor-car  standard  where 


in  which  d  is  the  diameter,  N  the  number  of  such  cylinders. 
Such  motors  usually  have  the  stroke  L  about  i.2d  and  turn  at 
1200  revolutions  per  minute,  but  the  formula  makes  no  allow- 
ances for  variation  of  mean  effective  pressure  with  fuel  variations. 
Frederic  Grover  proposed  to  recognize  the  relation  between 
the  compression  pressure  and  the  mean  effective  pressure  by 
calling 

M.E.P.  =  2  pb~  o.oi  p\ 

in  which  pb  is  the  compression  pressure  in  pounds  per  square 
inch.  (Fig.  205,  see  also  paragraph  201.)  It  will  be  true  when 
different  motors  are  compared,  which  are  working  on  the  same 
fuel,  but  the  variation  of  the  values  in  columns  15  and  16  of 
the  table  in  paragraph  29  will  show  the  inaccuracy  of  its  in- 
discriminate use.  It  will  be  correct  for  a  compression  pres- 
sure of  100  pounds  per  square  inch,  but  its  results  will  be  too 
high  below  this,  and  too  low  above  it.  In  the  intermediate 
class,  and  applicable  only  to  motors  using  the  same  fuel,  is  a 
formula  given  by  several  authorities  for  the  indicated  horse- 
power : 

<P  (I  +  c)  X  (Y— )  -i}\N 
I.H.P.  = VV    c    ' I 

9160 

In  this,  d  is  the  cylinder  diameter  in  inches;  /  the  stroke  in 
inches ;  c  the  length  of  the  clearance  space  in  per  cent  of  stroke, 

clearance  volume  .    .1  +  c       total  cylinder  volume 

or  -~         — - — : — — • ,  so  that  -  -  • 

piston  area  in  inches  c  clearance  volume 

N  =  Rev.  per  min. 


no 


THE  GAS-ENGINE. 


This  attempts  a  closer  approximation  by  recognizing  the  expo- 
nent of  the  expansion  and  compression  curve. 

4oa.  Computed  Cylinder  Volume,  Diameter  and  Stroke.*  — 
To  use  the  foregoing  discussion  for  computing  the  necessary 
area  of  cylinder  and  length  of  stroke,  it  should  be  noted  that 
the  gas-engine  cylinder  requires  a  clearance  volume  between  the 
piston  head  at  its  inner  dead  centre,  and  the  cover  or  head  of  the 
cylinder.  This  is  to  act  as  a  combustion  chamber  to  receive 
the  compressed  charge  and  to  provide  for  igniting  it.  This 
clearance  volume  has  only  an  effect  upon  the  mechanical  capacity 
of  the  motor  so  far  as  it  affects  the  compression  pressure  of  the 
mixture  of  fuel  and  air  before  ignition,  and  thereby  the  mean 
pressure.  It  must  be  computed  by  itself,  and  with  special 
reference  to  the  pressures  permissible  with  this  fuel  without 
pre- ignition.  It  is  treated  fully  in  paragraph  152.  The  diameter 
and  stroke  which  together  form  the  volume  displacement  of 
the  piston  are  directly  computable  from  the  foregoing  data 
already  found. 

The  design  is  practically  always  made  with  an  output  of  work 
in  foot-pounds  or  horse-power  demanded.  The  fuel  also  is 
given,  so  that  a  value  for  the  mean  effective  pressure  with  that 
fuel  is  derivable  from  the  table  in  paragraph  29  and  the  preceding 
discussion.  The  piston  speed  usual  in  motors  of  its  class  is  a 
conventional  outcome  of  experience  and  may  be  safely  assumed 
within  the  following  limits: 


Horse-Power  Capacity. 

Usual  Piston  Speeds, 
in  Feet  per  Minute. 

Average  Piston 
Speed  in  Feet 
per  Minute. 

Motor-car  cylinders  2-10  H.P.  per  cylinder 
Small  stationary  engines  less  than  30  H.P.  ... 
50—100  

600-1000 
450-700 
coo—  700 

%75o 

55° 
600 

ISO—  2<CO.  . 

600-800 

6sO 

500—600  

6<o—  S<o 

700 

700—000 

7^o 

700—1000 

800 

*  See  also  paragraph  202. 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  Iir 

These  standards  will  fix  the  value  of  the  quantity  LN  in  the 
horse-power  formula,  where  L  is  the  length  of  the  cylinder  and 
N  the  number  of  traverses  of  the  cylinder  which  the  piston 
makes  per  minute;  this  is  twice  its  number  of  revolutions  per 
minute.  In  the  four-cycle  or  Otto  type  of  single-cylinder,  single- 
acting  engine  (par.  62),  only  one  stroke  in  four  traverses  is  made 
under  working  or  effective  pressure:  the  formula  for  indicated 
horse-power  may  therefore  be  written 

I.H.P.  =      PLAS     , 

4  X  33000 

in  which  S  is  the  piston-speed  in  feet  per  minute  as  above,  and 
the  factor  4  appears  in  the  denominator.  The  factor  A  is  the 
effective  area,  or  the  gross  area  of  the  piston  diminished  by  the 
area  of  any  piston-rod  which  may  reduce  the  area  receiving  the 
pressure.  It  is  equal  to 

A  =  —  =  .7854  <P, 
4 

in  which  d  is  the  diameter  in  inches  if  the  mean  effective  pressure 
P  is  in  pounds  per  square  inch.  Hence,  if  there  are  n  cylinders, 
single-acting,  or  n  cylinder  ends,  in  operation  of  a  double-acting 

type  

=  J  I.H.P.          4  X  33000  i 

V  M.E.P.    '     .0.7854  X  5         n 

In  the  two-cycle  type  (par.  73),  an  effort  of  the  pressure  is 
exerted  once  in  every  two  traverses  of  the  piston,  and  the  factor  4 
becomes  2  giving  a  smaller  diameter  in  the  relation, 


d  =    J   I.H.P.  2    X   33000  £ 

V  M.E.P.    '    0.7854  X  S        n' 

In  most  cases,  the  designer  is  called  on  to  provide  that  his  engine 
shall  be  capable  of  overcoming  an  overload  demand  for  power. 
This  means  that  the  cylinder  diameter  shall  be  increased,  so 
that  under  such  demand  for  an  increased  horse-power  which 
is  a  percentage  /  of  the  normal  load,  the  engine  at  the  same 


112  THE  GAS-ENGINE. 

piston-speed  should  be  able  to  respond.     In  other  words  the 
normal  output  with  no  overload  is  to  be  increased  from 


I.H.P.  tofi  +-/-)l.H.P. 

\  100  / 


for  an  overload  of  /  per  cent  as  an  overload  factor.     Then  the 
formula  for  diameter  becomes 


I.H.P. 


100 '  4  X  33000         i 

M.E.P.  *  0.7854  XS       n 

for  the  four-phase  type,  and  the  corresponding  change  made  for 
the  two-phase  cycle. 

The  stroke  is  twice  the  crank-arm  length.  In  giving  the 
value  to  S  the  piston-speed  in  feet  per  minute,  the  length  of 
the  stroke  is  at  once  fixed  if  the  number  of  revolutions  has  been 
"specified.  Or,  the  conventions  of  a  relation  of  the  stroke  to  the 
cylinder  diameter  may  be  observed,  and  with  the  length  thus 
determined  the  factor  N  may  be  computed  and  the  revolutions 
per  minute  will  be  twice  N.  In  practice  the  latter  method 
gove.rns,  since  it  has  been  found  desirable  to  give  the  crank-arm 
a  considerable  leverage,  to  give  a  large  turning  moment,  and 
to  keep  the  diameter  less  than  the  stroke,  so  that  the  shock  of 
the  ignition  increase  of  pressure  shall  not  be  excessive  and  intro- 
duce inconvenient  vibration.  On  the  other  hand,  excessive 
crank  length  makes  a  long  and  bulky  engine,  and  the  power  is 
applie.d  obliquely  to  turn  the  crank  during  a  large  fraction  of 

the  stroke.     Hence  the  ratio  -  is  never  made  less  than  one,  nor 

d 

more  than  two;  in  motor-car  practice  it  is  from  i.o  to  1.3;  in 
small  stationary  engines  it  is  nearer  the  larger  limit,  while  in 
large  stationary  practice  the  ratio  is  settled  by  convenience 
anywhere  within  the  extremes.  A  study  of  the  engines  tested 
by  various  experimenters  and  reported  under  paragraph  177, 
will  show  the  trend  of  practice.  For  example: 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


Type  of 
Engine* 

Builder. 

Cylinder. 

Ratio 
I 
d 

H.P 

Rpm. 

No. 
Cyls. 

Diam. 
Inches. 

Stroke 
Inches. 

Motor-car 
Stationary 

4l 

8-5 
6.0 

13 
17 
14. 

51.18 
25 
29 
20.08 

40.55 

5* 
14 
12.5 

14 
24 

25 
55-12 

25 
40 

25-56 
51.24 

.22 
.64 
.08 
.08 
.41 

:% 

.0 

•4 
•3 
•3 

10 

10 

8 
86 
118 

IOO 

550 

900 

158 
281 
270 

'56 
160 
80 
180 
no 

150 
90 

4 

i 
i 

3 

i 
i 

Otto         

« 

^Westinghouse  

Crossley    

Schleicher  Schumm 
Cockerill    

41.  Graphical  Representation  of  the  Work  of  a  Piston- 
motor.  The  PV  Diagram. — Since  the  work  of  a  piston-motor 
is  the  product  of  the  two  factors,  pressure  in  pounds  multiplied 
by  feet  of  traverse,  it  is  obvious  that'a  closed  figure  can  be  drawn 
enclosing  an  area  which,  upon  an  assumed  scale  of  units,  shall  be 
the  same  as  the  given  product  in  foot-pounds.  Furthermore, 
whatever  the  shape  of  that  figure,  a  rectangle  of  equivalent  area 
can  be  drawn,  the  product  of  whose  base  into  its  altitude  shall 
p 


A  <—  PV 


FIG.  15. 

represent  that  same  number  of  foot-pounds  of  work.  If,  then, 
a  horizontal  line  be  drawn  from  an  assumed  origin  on  which  may 
be  measured  distances  in  feet  on  any  scale,  and  from  that  same 
origin  a  vertical  line  on  which  may  be  measured  pressures  on 


THE  GAS-ENGINE. 


an  appropriate  scale,  and  these  horizontal  units  be  designated 
by  V  and  vertical  units  by  P,  the  area  of  an  enclosed  figure  upon 
these  lines  as  coordinate  axes  will  reproduce  a  work  diagram 
of  a  piston-motor.  The  simplest  case  where  the  pressure  P  was 
constant  would  give  a  simple  rectangle  (Fig.  15).  If,  however, 
as  is  the  general  case,  the  pressure  is  not  constant,  the  curve 
which  forms  the  upper  line  of  such  a  diagram  (Fig.  16)  will  be 
a  curve  of  varying  ordinates,  and  it  will  be  necessary  by  means  of 
convenient  methods  to  get  an  ordinate  which  shall  be  the  mean 
of  all  ordinates  to  be  multiplied  by  the  length,  in  order  to  give 

the  actual  area.  If  the  appli- 
ance known  as  a  planimeter  is 
at  hand,  the  area  of  the  diagram 
can  be  ascertained  and  that  area 
divided  by  the  measured  length 
will  give  the  height  by  which 
the  length  is  to  be  multiplied 
in  order  to  give  an  area.  If 
a  planimeter  is  not  at  hand, 
the  length  of  the  diagram  can 
be  divided  into  a  convenient 
number  of  equal  parts  (say  ten)  (Fig.  16)  and  the  height  of  each 
partial  area  measured  by  the  scale.  The  total  of  these  partial 
heights  divided  by  their  number  gives  the  mean  height  by  which 
the  length  is  to  be  multiplied.  Or,  what  is  known  as  Simpson's 
rule  may  be  used. 

To  apply  Simpson's  rule  for  determining  an  area  the  diagram 
is  divided  vertically. by  ordinates.  The  first  one  is  called  p0  and 
the  last  one  pn.  Then  the  area  A  is  given  by  the  formula 


where  /  is  the  measured  length.     Dividing  this  area  by  the  length 
/,  the  mean  pressure  p  m  results,  or 
A 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  "5 

Such  a  diagram  (Fig.  16)  will  be  called  a  PV  diagram,  inas- 
much as  its  coordinate  factors  are  the  pressure  and  the  volume 
corresponding  to  one  stroke. 

42.  Gay-Lussac's  Law  for  Air.  —  It  was  found  by  the  physicist 
Gay-Lussac  that  atmospheric  air  increased  in  volume  by  ^|7  of 
itself  for  each  degree  centigrade.  In  the  Fahrenheit  scale  this 
fraction  becomes  T-g^.  If  this  be  expressed  in  symbols  and  v  is 
the  volume  at  any  temperature,  it  will  bear  to  its  volume  v9  at 
the  temperature  of  melting  ice  the  relation 


in  which  a  is  the  above  fraction,  and  /  is  the  range  above  the 
temperature  of  melting  ice.     The  equation  expressed  decimally 

is 

.00365    on  the  centigrade  scale 

and 

.002035  on  the  Fahrenheit  scale. 

By  the  expedient  of  heating  the  air  behind  a  piston  in  a  piston- 
motor  by  injecting  a  volume  of  gas  and  igniting  that  volume  in 
the  air,  it  will  be  apparent  that  a  great  increase  of  volume  tends 
to  occur,  and  that  this  increase  in  the  confined  space  will  be 
accompanied  by  the  increase  of  pressure  above  that  which  existed 
before  the  gas  was  ignited.  It  is  this  principle  which  is  used  in 
the  ordinary  types  of  piston  gas-motor  to  produce  the  pressure 
which  gives  the  desired  work.  It  is  obvious,  therefore,  that  the 
gas-engine  derives  its  capacity  for  doing  work  by  the  expansion 
of  air  caused  by  heat.  The  fundamental  conception,  therefore, 
of  the  PV  diagram  above  must  be  extended  to  take  account  of 
the  influence  on  the  air  which  results  from  changes  of  tempera- 
ture. 

43.  Law  of  Mariotte.  —  It  was  announced  by  Mariotte  in 
France,  in  1640,  and  by  Robert  Boyle  in  England,  independently, 
at  about  the  same  date,  that  :  The  temperature  of  the  gas  remain- 
ing constant,  the  volumes  of  the  same  weight  of  gas  at  different 
pressures  will  be  inversely  as  the  pressures.  Expressing  this 
law  by  symbols,  if  pQ  be  an  initial  pressure  expressed  in  any 
unit  of  pressure  on  a  unit  of  area,  and  VQ  the  corresponding  initial 


n  THE  GAS-ENGINE. 

volume  of  the  gas,  then  for  any  other  pressures  and  volumes 
p  and  v  which  come  together  it  will  be  true  that 

p0:p::v  :  v0; 
or,  more  conveniently, 

PQVO  =  pv  =  3i  constant, 

provided  no  change  of  temperature  or  heat  energy  occurs  by 
reason  of  processes  connected  with  such  change  of  volume.  It 
follows  further,  that  since  for  a  given  weight  of  gas  the  density 
will  vary  inversely  as  the  volume,  the  pressures  must  vary  directly 
as  the  densities,  and  will  be  directly  proportional  to  them  at  the 
same  temperatures.  Or,  in  symbols, 

pQ:p::DQ:D',     or,     ^=-^  =  a  constant. 

44.  Mariotte  and  Gay-Lussac  Law  Combined.  —  If  a  given 
weight  or  volume  of  gas  be  enclosed  in  a  cylinder  behind  a  piston 
and  the  pressure  and  volume  be  made  to  vary  by  moving  the  piston, 
it  will  follow  from  Mariotte'  s  law  alone,  using  the  same  symbols 
as  above,  that 


But   by  the  Gay-Lussac  law  the  volumes  varying  by  change  of 
temperature  of  the  gas  in  that  cylinder  would  give 


Hence  if  the  second  member  be  multiplied  by  the  appropriate 
value  for  the  pressure,  the  first  member  will  become 


and 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  117 

It  will  be  observed  that  the  first  members  of  these  last  equa- 
tions are  not  the  same  as  held  for  the  Mariotte  relation  alone. 

Dividing  one  by  the  other,  and  transposing  the  factors  p,  and 
dropping  the  primes,  since  they  both  correspond  to  the  changed 
condition  caused  by  the  addition  of  heat,  we  get 


For  a  its  value  in  either  thermometric  scale  may  be  substituted, 
so  that  the  equations  take  the  form 


.l&j  centigrade  readings, 
A 


or  the  form 


_ 
v2    p1     (461  + 

when  the  computation  is  made  from  the  zero  point  of  the  Fahren- 
heit scale. 

45.  Absolute  Temperature.  —  It  is  an  immediate  deduction 
from  the  law  of  Gay-Lussac  that  air  increases  by  ^rs  °f  its  volume 
at  zero  centigrade  for  each  degree  increase  of  temperature  to 
infer  that  with  each  degree  of  temperature  below  zero  the  vol- 
ume of  the  gas  should  be  diminished  by  that  same  fraction  of 
its  volume  at  zero.  It  follows,  therefore,  that  when  the  tem- 
perature has"  beeri  lowered  by  273°  the  equation  for  the  volume 
will  read 

^  =  1/0(273-273). 

This  is  equivalent  to  saying  that  at  this  temperature  the  energy 
resident  in  the  gas  to  cause  it  to  increase  its  volume  has  disappeared, 
or  has  become  zero.  Such  a  temperature,  therefore,  is  an  ideal 
point  from  which  all  temperature  can  be  counted  as  a  zero,  and 


118  THE  G/tS-ENGINE. 

for  this  reason  is  called  the  absolute  zero.  Temperatures  on 
the  ordinary  centigrade  scale  become  absolute  temperatures 
by  adding  273  to  the  reading  of  the  thermometer.  Similarly, 
for  Fahrenheit  degrees  they  become  absolute  readings  when  461 
is  added  to  the  thermometer  reading.  It  is  usual  to  designate 
the  reading  in  absolute  degrees  by  the  capital  letter  T.  If  this 
substitution  be  made  in  the  equations  of  paragraph  44,  they 
become 


v*    A    ZY 

which  may  be  transformed  so  as  to  read 

Mi     to 


T,        TV 

Each  of  the  members  of  this  equation  must  be  equal  to  the 
expression 

I   1  •':  v". -•      ~^'  .,..    : 

which  may  be  translated  to  say  that  at  constant  pressures  the 
volume  varies  directly  as  the  absolute  temperatures,  or  at  con- 
stant volumes  the  pressures  will  vary  directly  as  the  absolute 
temperatures.  The  law  of  Mariotte  says  that  when  the  absolute 
temperatures  are  constant,  the  product  of  pressure  multiplied 
into  volume  is  a  constant  for  any  given  condition  of  the  gas  at 
starting  with  respect  to  pressure  and  volume. 

The  advantage  of  the  use  of  the  absolute  temperature  in  com- 
putations and  formulae  is  that  it  makes  every  temperature  reading 
a  positive  reading  throughout  the  entire  range  of  experience  and 
practice,  and  eliminates  the  negative  reading  which  is  the  result 
of  the  location  of  the  zero  of  the  ordinary  stale  at  the  point  where 
water  freezes. 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  119 

It  is  also  of  advantage  in  enabling  the  energy  due  to  heat  in  a 
gas  to  be  compared  directly  with  the  energy  of  that  gas  under 
other  conditions. 

46.  Total  or  Intrinsic  Energy.  Available  Energy. — It  will 
be  apparent  from  the  discussion  in  the  previous  paragraph  that 
the  capacity  of  a  given  weight  of  gas  for  doing  work  against  a 
mechanical  resistance  will  be  measured,  first,  by  the  weight  of  the 
gas  or  the  amount  of  matter  present  in  it,  which,  by  definition, 
is  its  mass.  It  is,  secondly,  conditioned  by  the  amount  of  heat 
which  it  contains  when  that  amount  of  energy  is  measured  by 
counting  from  the  zero  on  the  absolute  scale.  It  is,  thirdly, 
measured  by  the  capacity  of  the  gas  for  the  absorbing  of  heat 
which  is  measured  by  the  quantity  of  heat  required  to  raise  the 
temperature  of  a  unit  weight  of  the  gas  by  one  degree  on  the 
thermometric  scale.  This  heat  capacity  of  the  gas  in  units  is 
called  its  specific  heat,  and  is  usually  designated  by  the  symbol  C, 
which  is  the  initial  of  the  French  word  chaleur.  If,  then,  the 
weight  of  the  gas  be  multiplied  by  its  specific  heat  and  by  the 
temperature  which  it  has  above  the  absolute  zero,  a  product 
results  which  is  the  expression  for  the  intrinsic  energy  which 
that  gas  has  under  those  conditions  and  without  having  that 
energy  artificially  increased.  In  symbols,  this  total  energy  is 
the  product  of 

WXCX  T= intrinsic  energy. 

It  will  be  observed  that  this  expression  does  not  contain  the 
pressure  under  which  the  gas  is  maintained  which  is  the  prac- 
tical shape  in  which  the  energy  is  made  manifest  as  discussed 
in  paragraph  40.  The  reason  for  this  is  that  there  are  only  two 
ways  in  which  the  pressure  can  be  increased.  The  first  is  by 
the  addition  of  heat  energy  to  the  given  weight  or  mass  of  gas 
which  will,  of  course,  increase  its  intrinsic  energy  by  increasing 
the  value  of  the  factor  T.  The  other  way  is  by  a  mechanical 
compression  due  to  a  force  exerted  to  compress  the  gas.  By 


120  THE  GAS-ENGINE. 

the  principles  of  the  conservation  of  energy  and  the  mechanical 
equivalent  of  heat  (par.  39)  this  mechanical  pressure  is  a  mani- 
festation of  heat  energy  in  another  form  or  can  be  replaced  by 
such  heat  energy;  and  the  mechanical  compression,  if  no  loss 
were  experienced,  would  reappear  in  the  compressed  gas  in  the 
form  of  an  increase  of  its  temperature.  For  this  reason  when 
comparing  two  states  of  the  gas,  it  is  their  difference  in  tempera- 
ture which  is  significant  as  respects  their  difference  in  energy 
and  not  their  difference  in  pressure. 

It  may  easily  happen  that  an  amount  of  intrinsic  energy  is 
not  available  for  the  doing  of  mechanical  work.  It  is  necessary 
in  the  continuous  operation  of  a  piston-motor  that  on  one  side  of 
it  shall  be  a  forward  pressure  driving  the  piston  and  overcoming 
resistance,  while  on  the  other  side,  which  may  be  called  the  nega- 
tive side  of  the  piston,  is  a  pressure  less  than  the  impelling  pressure, 
due  to  the  fact  that  that  side  of  the  piston  is  in  communication 
with  a  vessel  in  which  is  maintained  a  pressure  less  than  the 
impelling  pressure.  In  other  words,  if  the  pressure  on  both  sides 
of  the  piston  were  the  same,  there  would  be  no  impelling  energy 
to  overcome  the  external  resistance.  The  lowest  pressure  which 
can  be  produced  in  nature  is  that  which  results  when  the  atmos- 
pheric pressure  or  the  tension  of  the  atmospheric  air  is  removed 
from  a  vessel  by  the  creation  therein  of  a  Torricellian  vacuum. 
Under  ordinary  circumstances  the  negative  side  of  the  piston 
(and  in  gas-engine  practice  universally)  the  pressure  on  the 
negative  side  is  that  of  the  atmospheric  air  and  the  absolute 
temperature  that  of  the  atmospheric  air,  as  counted  from  the 
absolute  zero.  The  temperature  of  the  impelling  medium  must, 
therefore,  be  much  higher  than  the  temperature  of  the  air,  in 
order  that  it  may  have  an  energy  sufficient  to  do  the  required 
work  by  the  difference  in  temperature.  The  available  energy 
of  a  given  mass  of  gas  will  be  expressed  by  the  equation 


ENERGY  DUE   TO  EXPANSION   OF  GAS'  AND  AIR.  I2i 

in  which  W  is  the  weight  in  pounds  of  the  fuel,  Tl  is  the  tem- 
perature of  the  heated  air,  and  T2  is  the  temperature  of  the 
atmosphere,  or  that  to  which  the  heated  air  can  be  conveniently 
cooled  on  leaving  the  motor. 

The  more  applicable  form  of  this  for  gas-engine  practice  is 
to  take  the  weight  of  the  mixture  of  fuel  and  air,  the  latter  being 
the  quantity  computed  as  necessary  for  the  complete  combustion 
of  the  former  by  the  methods  of  paragraphs  13  and  29.  The 
calorific  power  of  the  fuel  is  supposed  to  go  into  raising  the 
temperature  of  its  own  mass  and  that  of  the  air  to  the  high 
temperature  7\  without  loss  or  transfer  to  other  or  surrounding 
objects,  and  to  do  this  without  doing  external  work  during  the 
process,  so  that  the  specific  heat  factor  is  that  for  a  constant 
volume  change.  Hence  the  mixture  will  be  i  4-  a,  and  if  its 
heat-energy  be  called  H,  it  will  be  true  that 

H  =  (i  +  a)  c,  (7\  -  T.). 

The  relation  therefore 


may  conveniently  be  compared  to  the  value  and  its  computation 
method  in  columns  15  and  16  of  the  table  in  paragraph  29, 
where  the  unit  is  the  cubic  foot  of  volume,  and  not  the  weight. 

47.  Efficiency.  Thermal  Efficiency.  —  The  term  efficiency 
applied  to  a  machine  or  to  an  engine  is  the  ratio  between  the 
available  energy  put  into  the  apparatus  and  the  energy  actually 
utilized  by  it.  This  ratio  is  expressed  by  a  fraction  whose 
numerator  is  the  energy  utilized  and  whose  denominator  is  the 
total  available  energy.  When  this  is  expressed  in  symbols  fora 
given  weight,  W,  and  a  given  value  for  the  specific  heat,  C,  it 
takes  the  form 

Efficiency  -  WCT*  ~  WCT* 


because  the  engine  rejects  at  the  exhaust  an  energy  WCT2  and 
can  therefore  only  have  utilized  the  difference  between  the 
energy  at  the  beginning  and  at  the  end  of  the  stroke.  Dividing 


I22  THE  GAS-ENGINE. 

out  the  common  factors  for  the  weight  and  specific  heat,  the 
equation   appears, 

T    —  T 
Thermal  efficiency  =  Et  =  - J-— —  —  . 

•  i 

This  is  an  expression  for  the  efficiency  of  a  heat-engine  first 
deduced  by  Carnot,  and  is  the  expression  for  the  best  result 
theoretically  obtainable  from  an  engine  operating  between  the 
two  temperatures  Tl  and  Tv  In  its  application  to  the  internal 
combustion  engine,  however,  it  must  be  noted  that,  as  dis- 
cussed in  the  previous  paragraph,  the  specific  heat  of  the 
combustion  process  is  cv  or  the  value  at  constant  volume,  while 
the  cooling  is  at  varying  volume,  or  at  the  constant  pressure 
conditions;  so  that  in  reality  the  formula  should  read: 

_  c,(T,  -  r.)  -  Cp  (T2  -  r.) 
«.  (r,  -  r.) 

If  the  ratio  of  these  two  specific  heats  (par.  54)  be  designated 
by  n,  this  becomes  on  simplification, 


But  this  is  applicable  only  to  a  type  of  combustion  motor  in 
which  no  energy  is  imparted  by  a  previous  compression.  This 
is  the  cycle  discussed  in  detail  under  paragraph  183  in  the  sequel, 
and  is  little  in  modern  use  by  reason  of  the  better  economy  of 
those  in  which  compression  occurs. 

For  the  latter,  another  temperature  is  of  greater  significance 
in  determining  the  efficiency,  which  may  be  called  Te,  and  is  due 
to  the  work  of  compressing  the  gas  from  the  initial  volume  Ff, 
to  the  final  or  compression  volume  F/.  The  computations  in 
paragraph  52  will  show  that  this  temperature  volume-pressure 
relation  will  be  given  by  the  equation: 

»—  i 


p  T, 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  123 

whence 


"p 

and 

c.(.Tt-T.)-e,(Tt-  r.)  Tt-  T 

~  " 


There  is  a  third  type  in  which  the  addition  of  heat  is  at  constant 
pressure  instead  of  at  constant  volume,  and  compression  is  used. 
Its  efficiency  equation  will  be 

cp  (T,  -  Tt)  -  cp  (r,  -  rt)  .         r,-r0 

cp  (Tl  -  r«)  Tl  -  Tc 

These  will  be  more  fully  and  exhaustively  discussed  in  the  sequel 
(pars.  183  to  200),  and  therefore  for  the  present,  attention  is 
directed  only  to  the  second  type  in  general  industrial  use.  If 
the  hypothesis  be  made  that  the  final  volume  after  expansion  is 
complete  is  the  same  as  the  mixture  had  before  compression 
began,  then  the  cooling  may  be  considered  as  taking  place  also 
at  constant  volume,  simplifying  the  equation  so  that  it  becomes 

c,  (T,  -  Tc)  -  c,  (Tt  -  r.)  _  r,-  T, 

c.Vi-T.)  .  2Y-ZV 

But  since  the  two  curves  of  temperature  range  may  both  be 
practically  considered  as  adiabatic  (par.  50)  and  with  the  volume- 
range  assumed  the  same 

T      T 

2> 


> 


Multiplying  both  terms  of  the  fractions  in  the  efficiency  equation 
by  Tc  and  substituting  for  T2  Te,  its  equal  Tl  T0,  factoring 
and  dividing  both  terms  by  Tt  —  Tc,  there  results 

T 
E,  -  i  -      *. 


124  THE   G4S-ENGINE. 

For  this  can  be  substituted  its  equal  from  the  foregoing  discussion 
in  either  of  the  forms: 

(V  \A 
~~r\     for  volumes 

or 

,.29 


IP  V29 

Et  =  i  —  (— -j     for  pressures. 
\fy' 


Substituting  this  value  for  E  in  the  equations  established  in  par- 
agraph 40,  the  expression  for  the  mean  effective  pressure  becomes 


M.E.P.  = 


From  this  the  mean  effective  pressure  for  design  may  be  com- 
puted when  the  compression  ratios  of  volumes  or  pressures  are 
fixed  or  assumed,  and  the  tabular  value  computed  in  paragraph 
29  inserted  for  the  fuel  to  be  used. 

47a.  Mechanical  Efficiency.  —  It  will  be  apparent  also  from 
an  inspection  and  study  of  the  energy  analysis  of  paragraph  ya, 
that  a  certain  amount  of  the  energy  of  the  motor  is  absorbed  in 
operating  its  own  functions,  and  in  mechanical  imperfections 
causing  loss.  These  absorptions  of  energy  will  always  make 
the  energy  computed  or  realized  in  the  cylinder  of  the  motor 
more  than  that  actually  delivered  for  useful  work  at  the  revolving 
shaft.  There  will  therefore  be  a  ratio  which  is  another  efficiency, 
existing  between  the  indicated  or  gross  or  cylinder  horse-power 
and  the  net  or  actual  or  brake  horse-power,  realized  when  the 
engine  is  tested  by  the  method  described  in  paragraph  170.  If  this 
efficiency  or  ratio  of  input  to  output  be  called  the  mechanical 
efficiency,  and  denoted  by  Em,  then 

,.,     _         Brake  Horse-Power  at  Shaft 

Indicated   Horse-  Power   in    Cylinder 
whence 

B.H.P.  =  Em  X  (I.H.P.). 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


I2S 


The  losses  which  cause  Em  to  have  a  considerable  value  are, 
first,  those  due  to  fluid  losses  in  friction  in  valve- pass  ages,  through 
carburating  apparatus,  exhaust  pipes  and  the  like;  in  inertia  of 
the  fluid  in  pipes,  passages  and  valves;  and  from  leakage  past 
piston  rings  and  valves.  Second,  those  due  to  mechanical 
friction  of  moving  parts.  These  latter  are  lessened  by  effective 
lubrication,  and  in  smaller  engines  such  as  used  in  motor  cars 
by  the  use  of  ball  or  roller  bearings.  The  fluid  friction  should 
be  inconsiderable,  say  from  5  to  6  per  cent  in  engines  which  are 
skilfully  designed,  with  small  leakage  and  low  velocity  of  flow 
through  valves,  passages  and  parts.  By  throttling,  however, 
and  the  action  of  governors  it  may  rise  to  30  or  35  per  cent,  and 
at  the  limit  become  equal  to  the  entire  capacity  of  the  engine 
reduced  intentionally  by  this  throttling  process. 

The  pre-compression  of  the  charge  which  is  practised  in  the 
two-cycle  type  of  engine  '(par-  73)  compels  a  mechanical  loss  to 
.overcome  the  resistance  to  compression,  which  is  not  recovered 
in  the  working  stroke.  This  loss  is  less  when  the  pre-compression 
is  done  by  the  motor  piston,  than  when  a  second  cylinder  is  used 
with  its  crank-pin  and  wrist-pin  losses.  In  small  engines  with 
simple  methods,  it  is  probably  10  per  cent;  in  larger  ones  with 
separate  pump  it  may  rise  to  30  per  cent,  and  forms  part  of 
the  price  paid  for  the  apparent  simplification  of  the  working  of 
the  system. 

Values  for  Em  will  probably  range  in  engines  of  different 
sizes  within  the  values  of  the  following  table. 


Capacity  of  Engine 
in  I.  H.  P. 

Four  Cycle. 

Two  Cycle. 

Percentage 
Loss. 

Value  of 

Em. 

Percentage 
Loss. 

Value  of 
Em. 

4-25 
25-500 
500  and  over 

20-26 
19-21 
14-19 

74-80 
79-81 
81-86 

27-30 
24-26 
27-30 

63-70 
64-66 
63-70 

The  loss  from  fluid  friction  effect  increases  necessarily  with 


126  THE  GAS-ENGINE. 

light  loads;  the  mechanical  friction  on  the  other  hand  usually 
increases  with  the  loads  and  as  pressures  increase.  If  the 
mechanical  fluid  and  unrestored  compression  losses  be  indicated 
by  Lm,  Lf,  and  Lc,  then 

Em  =  i  -  (Lm  +  Lf  +  Lc) 
and  B.H.P.  -  (i  -  Lm  -  Lf  -  Lc)  I.H.P. 

47b.  Combined  Mechanical  and  Thermal  Efficiency.  The 
Guarantee.  —  A  desirable  tendency  of  recent  contracts  between 
the  maker  of  internal  combustion  engines  and  their  buyers 
has  been  to  base  the  agreement  on  the  output  of  horse-power 
per  heat  unit  of  the  fuel  to  be  supplied.  The  unit  of  fuel 
multiplied  by  its  price  is  the  investment  which  the  user  is  to 
make,  the  interest  on  which  is  the  return  in  horse-power  which 
he  is  to  receive.  If  both  parties  use  the  units  in  the  same 
sense  this  understanding  is  in  every  way  defensible,  eliminating 
all  questions  of  opinion,  assertion  or  controversy,  and  leaving 
only  a  possible  discussion  on  facts  which  are  easily  proven  to 
the  satisfaction  of  both  parties.  But  it  will  be  apparent  that  a 
guarantee  of  economy  based  on  the  relation  of  output  to  input 
as  discussed  in  the  foregoing  sections  must  be  clearly  under- 
stood by  both  buyer  and  seller  to  prevent  regrettable  confusion. 
For  if  the  formula  on  which  the  agreement  is  based  be  merely 
stated : 

F  ~  .          _  Horse-power  or  foot-pounds  per  minute 
B.T.U.  per  minute  of  fuel  X  778 

it  is  apparent  that  there  may  be  two  understandings  as  to  the 
value  of  the  numerator,  and  two  interpretations  of  the  value  of 
the  denominator.  If,  for  example,  the  indicated  horse-power  be 
used  in  the  numerator  by  one  party  and  the  brake  horse-power 
by  the  other;  or  the  low  fuel  value  be  used  in  the  denominator 
by  one  and  the  high  fuel  value  be  used  by  the  other,  there 
are  four  different  guarantees  all  correct  in  fact  and  theory. 
That  is,  it  is  true  to  place 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND   AIR. 

E  =  _  B.H.P.  X  33000  _ 
1       B.T.U.  in  fuel  per  minute  (high)  X  778 
B.H.P.  X  33000 


E 

mi 


_ 
B.T.U.  in  fuel  per  minute  (low)  X  778 


E      =  I.H.P.  X  33000 


E    .= 


B.T.U.  in  fuel  per  minute  (high)  X  778 
I.H.P.   X  33000 


B.T.U.  in  fuel  per  minute  (low)  X  778 
From  this,  the  last  or  Eh  is  the  highest  guarantee  and  will  there- 
fore be  that  preferred  by  the  seller  in  evaluating  his  product;  the 
first  one  is  the  lowest,  and  will  be  that  naturally  used  by  a  dis- 
satisfied buyer.  The  seller  put  on  the  defensive  will  claim  his 
product  satisfactory  if  it  meets  the  value  of  £,;  while  the  buyer 
really  supposed  he  was  to  get  the  value  of  Eh.  It  would  appear 
that  justice  to  both  parties  was  best  secured  by  the  use  of  one 
of  the  intermediate  ones,  and  there  is  less  ground  for  contro- 
versy where  tests  can  be  made  by  absorbing  or  transmitting 
the  power  actually  delivered,  by  the  use  of  Emi.  Where  the 
engine  is  too  large  to  test,  or  is  to  be  applied  to  uses  where  power- 
tests  would  be  inconvenient,  then  the  value  in  Em2  can  be  agreed 
to.  The  lower  fuel  value  is  that  actually  available  in  the  hot- 
engine  cylinder,  and  is  the  fairest  for  both  parties. 

If,  for  example,  an  engine  be  assumed,  working  on  a  fuel  of 
600  B.T.U.  per  cubic  foot  (high)  and  of  550  B.T.U.  (low)  (pars. 
15  and  29),  and  that  it  uses  for  facility  in  computation  1000 
cubic  feet  per  hour,  giving  a  brake-horse-power  of  40,  and  an 
indicated  horse-  power  of  50,  then  the  ideal  computations  for 
the  four  efficiencies  would  be: 

„       40  X  33000  X    60       132  , 

EI  =  -         J0  -  =  —^  =  17  per  cent  nearly. 

1000  X  600  X  778       778 


<  330ooX6o  =^  =  I8  per  cent 


1000  X  550  X  778      778 

E      _SQ  X  33000  X    6o_  165  _gi 
'm2       1000  X  600  X  778      778 

^         so  X  33000  X    60      180 

Eh  =  —  = =  23  per  cent, 

1000  X  550  X  778      778 


128  THE  GAS-ENGINE. 

It  will  have  been  noted  in  paragraph  39  that  the  ratio  of  the 
B.T.U.  to  the  foot-pound  was  778,  so  that  one  horse-power  per 
hour  or  60  X  33000  =  1980000  foot-pounds  per  hour  should 


be  the  output  of      -          =  2545  B.T.U.  if  there  were  no  losses. 

778 

But  from  paragraph  47  the  inevitable  loss  from  defective  tem- 
perature range  was: 


Hence  the 

B.T.U.  (low)  per  ..H.P.  per  hour 


if  the  theoretical  mean  pressure  is  realized  in  the  cylinder.  But 
the  actual  engine  never  succeeds  in  reaching  this,  but  reaches 
instead  a  pressure  Pf  =  fP.  That  is,  the  actual  work  diagram 
falls  inside  of  the  theoretical  one  by  a  percentage  /.  If  this 
includes  the  difference  also  between  the  indicated  and  brake. 
horse-power  results,  the  formula  for  the  guarantee  becomes: 

B.T.U.  (low)  per  B.H.P.  per  hour  =  25^        X  /. 

•  T  —  I     M 


The  computation  of  the  value  to  be  given  to  the  factor  /  in 
design  will  be  taken  up  further  in  paragraphs  201,  202.     The 

Pf 
quantity/  =  —applied  to  a  work  or  indicator  diagram  is  called 

the  diagram  factor,  and  indicates  how  much  larger  its  area 
should  be  than  that  imposed  by  pure  computation  from  theo- 
retical data. 

48.   Expansive    Working   of    Media    Compared   with   Non- 

expansive  Working.  —  It  will  be  apparent  from  the  foregoing 
equation  that  the  efficiency  increases  with  the  difference  between 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


129 


the  initial  state  of  the  gas  and  its  terminal  state  as  to  tempera- 
ture. When  these  temperatures  are  accompanied,  as  is  usually 
the  case  with  a  corresponding  pressure,  it  becomes  apparent 

that  with  a  diminution  of  tem- 
perature comes  a  diminution 
of  pressure.  The  diagram 
(Fig.  17),  similar  to  that  in 
paragraph  40,  shows  that  at 
the  end  of  the  stroke  of  the 
piston  in  the  cylinder  the  pres- 
sure has  materially  fallen,  so 
that  when  the  exhaust-valve 
opens  and  empties  the  contents 
of  the  cylinder  into  the  open 
air  there  is  less  energy  rejected 
than  if  that  terminal  pressure 
were  more  nearly  that  which 
prevails  at  the  beginning  of  the 
stroke.  This  indicates,  there- 
fore, that  it  is  of  manifest 


FIG.  17. 


advantage  to  cause  the  medium  to  expand  in  the  cylinder  while 
driving  the  piston  so  that  it  shall  change  from  an  amount  of 
intrinsic  energy  at  the  beginning  of  the  stroke  to  one  which  is  as 
far  reduced  at  the  end  of  the  stroke  as  is  consistent  with  a  margin 
of  impelling  force  to  overcome  any  resistance  caused  by  back 
pressure  on  the  negative  side.  Such  an  operation  of  the  medium 
secures  a  more  complete  utilization  of  the  heat  energy  by  the 
considerable  change  in  the  amount  of  such  energy  from  the 
beginning  to  the  end  of  the  stroke,  which  energy  should,  of  course, 
appear  in  overcoming  the  resistance  at  the  crank-pin  of  the 
engine.  Not  only  is  the  energy  more  completely  utilized  and  a 
less  amount  of  it  rejected  with  the  exhausted  air,  but  the  noise 
incident  to  the  discharge  of  the  exhausted  gases  is  diminished 
and  there  is  a  tendency  to  diminish  the  back  or  negative  pressure 
for  the  succeeding  stroke.  It  will  be  found  that  expansive  work- 
ing is  a  feature  of  all  important  heat-engines. 


130 


THE   GAS-ENGINE. 


4Q.  Isothermal  Expansion. — The  most  natural  condition 
for  expansion  is  that  in  which  the  fall  of  pressure  occurs  with 
increase  of  volume  in"  the  PV  diagram,  accompanied  with  a  drop 
in  temperature  incident  to  the  external  work  which  the  gas  is 
doing  as  it  acts  upon  the  piston.  If,  however,  by  surrounding 
the  cylinder  with  a  provision  to  maintain  its  temperature  the  gas 
expands  without  drop  in  temperature,  due  to  the  external  work, 
but  has  the  same  amount  of  intrinsic  energy  at  the  end  of  the 
stroke  as  it  had  at  the  beginning,  it  will  be  exhausted  from  the 
cylinder  at  the  same  temperature  at  which  it  came  in.  An  ex- 
pansion which  takes  place  without  change  of  the  temperature  is 
called  an  " isothermal"  expansion,  since. the  heat  is  equal  at  all 
points  of  the  stroke.  The  heat  necessary  to  do  the  mechanical 
work  of  that  stroke  has  been  supplied  from  the  appliance  outside 
the  cylinder  which  maintained  its  heat,  and  not  by  the  heat  of 
the  expanding  gas  which  is  within  the  cylinder. 

The  mass  working  in  the  cylinder  carried  out  with  its  exhaust 
as  much  heat  as  it  took  in,  and  so  far  as  heat  is  concerned  that 
heat  is  wasted.  Such  expansion 
follows  the  Mariotte  law  by  defi- 
nition, so  that  (Fig.  18) 


This  law. may  be  expressed  graph- 
ically by  the  curve  of  an  equilateral 
hyperbola    referred    to    the    coor- 
dinate  axes    of    pressure  and  vol- 
ume   as    asymptotes.     The    work  FlG-  l8- 
done  by  the  PV  diagram  under  the  curve  of  the  hyperbola  will  be 
expressed  by  the  differential  equation 


If  this  expression  be  integrated  by  the  methods  of  the  calculus 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  131 

betwee'n  the  limits  v^  corresponding  to  the  initial  volume,  and  v2J 
corresponding  to  the  final  volume  at  the  end  of  the  stroke, 


•  loS-  IT- 


It  will  be  obvious  that  isothermal  expansion  will  be  of  lim 
ited  significance  in  gas-engine  practice. 

50.  Adiabatic  Expansion. — The  more  natural  and  usual 
form  of  expansion  takes  place  when  there  is  no  means  of  keeping 
up  the  temperature  of  the  gas  in  the  cylinder  as  it  expands,  but 
in  which  the  gas  cools  by  an  amount  equivalent  in  heat-units  to 
the  external  work  overcome  by  the  piston  when  driven  by  such 
expanding  gas.  This  kind  of  expansion  is  called  adiabatic  since 
there  is  no  transfer  or  passage  of  heat  through  the  cylinder- walls 
to  the  gas,  but  it  operates  by  the  expenditure  of  its  intrinsic  energy 
in  overcoming  the  resistance.  It  is  obvious  that  such  expansion 
will  be  accompanied  by  a  change  in  the  ratio  of  the  pressure 

to  the  volume,  so  that  at  the  end 
of  the  stroke  the  pressure  will  be 
less  than  it  would  have  been  with 
isothermal  expansion  by  the  with- 
drawal of  the  heat  represented 
by  the  overcoming  of  the  mechan- 
ical resistance.  This  is  expressed 


rin  symbols  by  giving  to  the  factor 
v 


an  exponent  greater  than  unity. 
If  that  exponent  be  designated 
by  n,  then  the  expression  pv 

attaching  to  isothermal  expansion  becomes  pvn  when  applied 
to  adiabatic  expansion.  A  corresponding  integration  of  the 
expression 


W 


fvz 

=  /     pdv 

t/w. 


132  THE  GAS-ENGINE. 

b  ecomes 


which  is  more  conveniently  written 


If  the  ratio  between  the  initial  volume  V1  and  the  final  volume 
v2  be  denoted  by  r,  then  this  becomes 


-i 


The  condition  in  the  internal  combustion  engine  is  always  that 
in  which  an  initial  volume  filling  the  clearance  or  combustion 
chamber  partakes  also  of  the  expansion.  The  real  ratio  of 

expansion  is  therefore  that  of  -  -  —  whose  reciprocal  is  - 

v2  -  vt  r  —  i. 

The  area  of  the  diagram  being  the  work  done  in  one  stroke, 
and  this  area  being  equal  to  one  whose  length  is  that  of  the 
stroke  of  the  piston  and  whose  height  is  the  mean  pressure 
exerted  over  that  area,  the  mean  pressure  will  be  found  by  divid- 
ing the  work  area  by  the  length  which  is  vn  ;  hence,  when  there  is 
no  back  pressure 

' 


... 

v2      n  —  i     r  —  il        r  —  i 

51.  Adiabatic  Work  in  Terms  of  Pressures.  —  It  is  some- 
times convenient,  instead  of  expressing  the  work  in  adiabatic 
expansion  in  terms  of  volumes,  to  express  this  work  in  terms  of 
the  range  of  pressures  between  the  beginning  and  the  end  of  the 
stroke.  The  computation  for  this  is  as  follows: 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  133 

Since 

A»W  =  AW.",     then    |  =  ^, 

whence  by  extracting  the  nth  root 


and  by  raising  both  members  to  the  n  —  i  power, 


Hence  the  equation  for  work  of  expansion  of  the  preceding  para 
graph  becomes 


52.  Temperature  Change    in  Adiabatic    Expansion.  —  Since 
in  adiabatic  expansion 


Multiplying  both  sides  by  —  ,  we  have 


But  (par.  54) 


134  THE  GAS-ENGINE. 

hence 


But  the  previous  paragraph  has  shown 

s 

fz\*~*'  (h\  . 

vV       W     ' 


hence 


n  —  i 
n 


Which  can  be  substituted  in  either  of  the  previous  expressions, 
giving 


53.  Other  Thermal  Lines.     Isometric.     Isopiestic.     Isobars. 

— Since  the  pressure,  volume,  and  temperature  are  the  three 
attributes  of  a  gas  which  can  be  caused  to  vary  by  variation  in 
the  heat-energy,  the  isothermal  and  adiabatic  curves  are  not  the 
only  lines  which  may  be  used  upon  the  PV  plane  to  represent 
changes  in  the  gas.  It  is  apparent  that  a  given  volume  or  weight 
of  the  gas  may  be  enclosed  in  a  vessel  or  chamber,  and  without 
increase  in  its  volume  its  pressure  may  be  increased  by  the  addi- 
tion of  heat.  Such  increase  in  pressure,  without  increase  of 
volume,  would  be  represented  on  the  PV  plane  by  a  vertical 
line  at  right  angles  to  the  axes  of  volume  and  parallel  to  the  axes 
of  pressure.  It  would  be  designated  as  an  isometric  line,  and 
is  that  which  is  traced  when  the  gas  in  a  gas-engine  cylinder  is 
ignited  while  the  piston  stands  at  the  dead-centre.  It  is  called 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


135 


an  isometric  line  (Tig.  20).  When,  on  the  other  hand,  the  change 
of  condition  in  the  gas  is  a  change  in  its  volume,  without  change 
in  its  pressure,  then  a  horizontal  line  parallel  to  the  axes  of  volumes 
at  a  height  proportional  to  the  constant  pressure  above  that 


aa, 


15, -> 


( -15  „----* 


FIG.  20. 


FIG.  21. 


axis  will  represent  the  variations  in  volume  as  it  increases  or 
decreases.  Such  a  line  is  called  an  isopiestic  line  or  an  isobar 
(Fig.  21).  Such  a  line  represents  the  condition  when  the  piston 
is  either  drawing  in  its  mixture  of  gas  and  air  into  the  cylinder, 
or  is  expelling  the  products  of  combustion  after  the  working 
stroke  when  the  areas  of  the  valves  are  sufficient  so  that  no  varia- 
tion of  pressure  occurs  during  such  change  of  volume  occupied 
by  the  gas. 

It  is  further  apparent  that  if  neither  pressure,  volume,  nor 
temperature  remain  constant,  but  all  are  caused  to  vary,  a  curve 
may  be  determined  by  experiment  or  observation  which  shall 
represent  on  thePF  plane  the  variations  of  pressure  and  volume, 
even  when  these  do  not  follow  any  law  which  is  capable  of  graph- 
ical delineation  in  advance.  The  curves,  in  any  case,  are  curves 
of  the  relation  between  the  values  of  two  quantities  and  are, 
therefore,  capable  of  being  expressed  analytically  by  an  equation 
which  will  be  either  that  of  a  straight  line  or  of  a  curve.  Applica- 
tions of  these  thermal  lines  will  appear  in  Chapter  XVII. 


136  THE  GAS-ENGINE. 

54.  Specific  Heat  at  Constant  Pressure  and  at  Constant 
Volume.  —  In  the  equation  resulting  from  the  combination  of 
the  two  laws  of  Mariotte  and  Gay-Lussac,  the  expression  appears, 


_ 

T      ~    T    * 

•*•  i         •*•  o 

It  will  be  usual  that  the  pressure,  volume,  and  temperature 
corresponding  to  the  condition  of  the  subscript  zero  will  be  the 
volume  occupied  by  a  unit  weight  of  the  substance  (probably 
one  pound)  at  a  pressure  p^  which  will  denote  the  pressure  on  a 
square  foot  when  the  barometer  reads  30  inches  of  mercury  at 
the  sea-level  and  the  temperature  T0  is  that  corresponding  to 
the  absolute  temperature  at  which  ice  melts.  These  values  for 
the  second  member  of  the  equation  are  not  variables,  but  are 
matters  of  definite  observation  and  are  constants  of  nature.  If 
the  second  member  of  that  equation,  therefore,  be  designated  by 
the  symbol  R,  the  equation  can  be  written 


The  value  for  R  for  atmospheric  air  is  easily  calculated  when 
it  is  recognized  that  it  represents  the  increase  in  the  value  of  the 
product  poV0  when  T  is  raised  from  zero  degree  Centigrade  to 
one  degree.  Let  a  cylinder  be  imagined  having  a  square  foot 
of  area  in  which  fits  a  weightless  piston,  loaded  with  a  weight 
of  14.7  pounds  per  square  inch,  which  is  the  pressure  at  the 
atmosphere  at  sea-level,  when  the  barometer  reads  30  inches  of 
mercury.  The  total  pressure  will  then  be  14.7X144=2116.5 
pounds.  If  the  piston  enclose  below  it  a  cubic  foot  of  air  and 
this  cubic  foot  be  expanded  by  heat  until  it  occupies  a  space  of 
two  cubic  feet,  the  work  in  foot-pounds  done  by  the  cubic  foot  of 
air  will  be  2116.5  foot-pounds.  Since  the  cubic  foot  of  air  at 
these  conditions  weighs  .080728  pound,  the  work  done  by  one 
pound  will  be 

2116.5 


.080728 


=  26217.66  foot-pounds 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  13 7 

by  one  pound  of  air.  The  Gay-Lussac  law  says  that  to  double 
the  volume  of  the  gas  requires  an  addition  of  273°  Centigrade, 
or  493°  F.;  hence  the  outer  work  which  will  be  expended  when 
the  temperature  is  raised  one  degree  will  be  ^  of  that  expended 
in  raising  it  493°,  so  that  the  outer  work  entailed  by  the  rise  of 
one  degree  temperature  Fahrenheit  will  be 

26217.66     MQ  R 

.„-       -  T   -53'354— -K. 

493  |  o 

Values  of  R  can  be  similarly  calculated  for  any  other  medium 
when  the  weight  per  cubic  foot  and  the  coefficient  of  expansion 
by  heat  are  known.  It  is  customary  to  describe  a  gas  for  which 
the  value  of  R  remains  constant  throughout  all  usual  ranges  of 
temperature  by  the  term  permanent  gas.  Where  the  gas  can  be 
made  liquid  by  pressure  or  lowering  of  its  temperature,  or  both, 
the  value  of  R  becomes  uncertain  near  the  point  of  such  lique- 
faction. 

In  the  foregoing  deduction  the  volume  was  supposed  to  be 
variable  and  the  pressure  constant  when  the  heat  was  applied. 
It  took  a  certain  amount  of  heat  to  increase  that  volume  over- 
coming that  constant  pressure  and  a  certain  amount  of  heat 
received  by  the  gas  was  expended  in  doing  that  external  work. 
If,  on  the  other  hand,  the  gas  had  been  enclosed  in  an  inelastic 
vessel  so  that  the  gas  could  not  expand  by  action  of  the  heat, 
it  is  obvious  that  its  temperature  for  a  given  application  of  heat 
would  have  been  higher,  inasmuch  as  no  expenditure  of  heat 
energy  took  place  and  disappeared  in  overcoming  the  external 
resistance.  Since  the  specific  heat  of  a  substance  is  the  amount 
of  heat  required  to  raise  a  given  weight  one  degree,  it  becomes 
apparent  that  there  are  two  specific  heats  for  gases:  the  specific 
heat  at  constant  pressure,  which  was  concerned  in  the  process 
described  for  obtaining  a  value  for  R  and  which  is  designated 
by  the  initial  CP,  and  the  specific  heat  at  constant  volume  with 
variable  pressure  which  is  represented  by  the  initial  Cv.  It 


T38  THE   G4S-ENGINE. 

will  be  apparent  that  the  specific  heat  at  constant  pressure  will 
always  be  the  larger  value,  since  the  external  work  in  foot-pounds 
denoted  by  R  divided  by  the  foot-pounds  corresponding  to  one 
heat-unit  should  be  equal  to  the  difference  in  the  specific  heats; 
or,  in  symbols, 

R 


Regnault's  experiments  gave  for  Cv  the  value  0.1691;   for  Cp 
his  value  is  0.2375;   hence 


7^=-^  =  i.4o8-w. 
Cv     1691 

In  gas-engine  practice  in  which  the  working  medium  is  a 
mixture  of  air  with  other  gases,  the  value  of  this  ratio  will  be 
different  and  should  be  a  matter  of  experiment.  This  ratio  will 
be  the  exponent  which  should  be  used  in  computations  involving 
the  expansion  or  compression  of  the  medium  which  exponent 
has  been  designated  in  the  preceding  paragraph  by  the  symbol  n. 

The  condition  of  increasing  volume  with  the  pressure  con- 
stant is  the  more  desirable  condition  in  heat-engines  since  the 
value  for  the  mean  pressure  in  the  formula  for  work  in  terms 
of  horse-power  is  greater  and  the  weight  of  gas  in  the  cylinder 
carries  more  heat  and  more  energy.  The  specific  heat  at  constant 
volume  has  been  called  the  real  specific  heat  and  the  specific 
heat  at  constant  pressure  the  apparent  specific  heat,  since  there 
is  no  means  conveniently  at  hand  of  exactly  evaluating  the  equiv- 
alent for  the  outside  work  done  and  expended  in  overcoming 
mechanical  resistance. 

When  a  gas  is  heated  from  a  temperature  absolute  7\  to 
another  higher  absolute  temperature  T2)  under  a  constant  pressure, 
the  external  work  done  will  be  that  of  overcoming  the  pressure 
ihrough  a  space  represented  by  the  difference  between  the  volume 
•vl  at  the  temperature  7\  and  the  volume  v2  which  corresponds  to 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 

the  temperature  T2.    The  mechanical  work  done  will  be,  there- 
fore, 


which  must  be  equal  to  the  expression 


The  heat  taken  in  under  this  condition  per  pound  of  the  gas  will 
be 

C'P(T2-T^  in  heat-units, 

which  can  be  transformed  into  work-units  by  multiplying  by  778. 
The  difference  in  intrinsic  energy  will  be  the  difference  between 
these  two  quantities,  and  may  be  written 


When,  on  the  other  hand,  the  same  weight  of  gas  (one  pound) 
was  heated  at  constant  volume  from  T1  to  T2  the  heat  taken  in 
is  expressed  by 

C&-T& 

since  no  external  work  is  done,  and  the  whole  applied  heat-energy 
goes  to  store  up  internal  energy.  But  if  it  be  assumed  that  the 
same  amount  of  heat-energy  was  applied  to  the  gas  in  the  two 
cases,  so  that 

CB(ra-7\)  should  equal  (n*Cp-R)     (T9-TJ9 
the  expression  simplifies  into 


as  was  just  shown  above. 

It  may,  therefore,  be  stated  that  the  expression  Cw(jT2  —  T^) 
expresses  or  measures  the  change  of  internal  energy  in  a  unit 
weight  of  gas  in  changing  its  temperature  from  Tl  to  T2  in  any 
manner,  no  matter  how  the  volume  or  pressure  may  vary  during 
the  process. 


THE  GAS-ENGINE. 

It  may  be  of  interest  to  compute  the  temperature  and  pressure 
in  a  gas-engine  cylinder  due  to  the  ignition  of  the  weight  of  com- 
bustible mixture  which  has  been  drawn  in  at  atmospheric  pressure 
pi\  compressed  to  its  final  volume  vf  and  pressure  pj  and  is 
then  ignited  at  constant  volume. 

From  paragraphs  29  and  46,  the  calorific  value  of  the  cubic 

TT 

foot  of  such  mixture  at  atmospheric  pressure  was  -  in  which 

i  +  a 

a  is  the  volume  of  non-fuel  elements,  which  are  added  to  secure 
combustion  of  the  unit  volume  of  fuel.  The  volume  is  changed 
by  compression  to  vf  and  the  temperature  at  the  end  of  the 
compression  is  called  Tc  (par.  47),  and  is  (par.  52) 


Therefore  the  value  of  Tc  being  known  by  computation,  the 
heat  of  combustion  when  H  and  the  quantity  (i  +  a)  are  reduced 
from  their  volume  values  per  cubic  foot  to  the  corresponding 
quantities  in  pounds,  will  be  given  by  the  equation  : 


TT 

whence  (7\  —  T8) 


C,  (i  +  a) 

TT 

The  quantity is  given  in  cubic  foot  values  for  a  wide  range 

of  fuels  in  column  15  of  the  table  in  paragraph  29.  The  value 
of  Cv  is  given  above.  Hence  the  range  above  the  compression 
temperature  is  at  once  given  when  the  data  are  reduced  to  pounds. 
The  corresponding  pressure  is  (par.  44) : 

T 

#,  -  h-^ 

1  3 

since  the  volume  and  weight  do  not  change  by  the  condition 
imposed. 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


55.  Effective  Specific  Heat. — In  the  gas-engine  problem, 
however,  the  gas  is  not  a  simple  element  or  a  stable  chemical 
combination,  but  is  a  mixture  of  varying  proportions  and  of  vary- 
ing constituents.  Serious  error  will  result  from  a  disregard  of 
the  difficulties  introduced  by  these  phenomena.  For  example,  if 
the  combustion  is  direct,  so  that  a  pound  of  carbon  burns  to 
carbon  dioxide,  the  CO2  gas  has  a  volume  at  32°  according  to 
the  following  table  of  8.102  cubic  feet: 


I 

2 

3 

4 

5 

6 

7 

8 

1 

1 

Gas. 

Specific 
Gravity. 

Pounds  per 
Cubic  Foot. 

Cubic 
Feet  per 
Pound. 

Specific 
Heat  at 
Constant 
Pres- 
sure. 

Specific 
Heat  at 
Constant 
Volume. 

Ratio 

f'-°- 

Oy 

I 

Air 

I    OOOO 

O  080728 

12    387 

O    237^ 

o  1689 

406 

2 

Oxygen   .  .  . 

I     105  1 

O    089  2  1 

1  1    209 

O    217^ 

O    I  ?  ^ 

4O3 

Hydrogen      .  .  . 

o  060^ 

o  oo  561 

178    2  3 

34OO 

u-  *;>j 

2    406 

417 

Nitrogen 

o  0714. 

o  0^842 

12    7^2 

O    244 

O    1*71 

4OQ 

6 

7 

Carbon  monoxide,  CO 
Carbon  dioxide,  CO2  . 
IVIarsh-gas,  CHi 

0.9674 
1.5290 

o  ^  ^60 

0.07810 

0.12343 

o  04488 

12.804 
8.102 

0.245 

0.216 

O    ?O7 

0-^3 
0.171 

.416 
.165 

27 

8 

Ethylene,  C2H4 

o  0847 

O    O7Q4Q 

12     ^80 

w-  jy6 

O    332 

144 

Steam  . 

O    O37Q4 

26    42 

v-JJ-* 

o   360 

•3Q2 

•a**1 

Nos.  1-8  at  atmospheric  pressure  and  at  temperature  of  melting  ice.     Steam 
at  212°  F. 

But  if  the  gas  was  first  made  into  CO,  and  an  extra  volume 
of  oxygen  supplied  to  burn  the  one  pound  of  CO  into  CO2,  the 
proportions  of  mixture  would  be 

CO       +O  =  CO2ofwhichCO=  —  =  -Z- 

44     ii 

12+16+16=    44        and       O=  — = — 

44     ii 

the  volume  of  the  mixture  would  be 


and 


—  of  1 2. 804=  8.148 
ii 


—  of  1 1. 200=  4.076 

ii  — '— 

Total  =  12. 224 


142  THE  GAS-ENGINE, 

making  a  volume  quite  different  from  that  resulting  from  the 
single-  step  process.  Hence  the  proper  value  to  be  inserted  in 

y 

the  formula  for  the  increase  in  temperature  for  the  quantity  —  ;  — 

in  that  expression  does  not  always  readily  appear  in  advance 
from  theoretical  considerations.  But  as  a  matter  of  fact,  the  value 
to  be  inserted  for  the  factor  representing  the  specific  heat  in  that 
formula  (par.  14)  is  still  more  uncertain.  The  air  supporting 
combustion  is  gradually  passing  through  a  series  of  changes 
throughout  the  working  stroke,  and  these  changes  doubtless  in- 
volve molecular  rearrangement  in  transit.  Furthermore,  the 
experiments  of  the  physicist  have  shown  that  the  specific  heat 
is  not  a  constant  for  all  temperatures  of  a  gas  or  a  mixture,  but 
increases  with  the  temperature  according  to  some  law  whose 
form  takes  the  shape  for  specific  heat  at  constant  volume: 


So  that  at  a  higher  temperature,  T2,  the  specific  heat  is  greater  than 
at  the  lower  temperature,  7\,  by  a  small  but  as  yet  undetermined 
amount  proportional  to  the  difference  between  the  temperatures. 

Hence  the  present  practice  is  to  approximate  to  the  actual 
values  of  the  factor  which  may  be  called  the  effective  specific  heat 
by  one  of  five  methods. 

The  first  method  will  be  by  the  use  of  what  is  designated  as 
Grashof's  formula,  which  assumes  all  gases  to  have  the  same 
chemical  composition,  and  that  the  letter  R  denotes  the  ratio 
of  gas  to  air  in  the  mixture.  For  the  specific  heat  at  constant 
volume, 

[0.169X^1+0.286 
£+0.48 

for  specific  heat  at  constant  pressure, 

[0.2375X^1+0.343 
^p~          12+6.48 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR,  143 

in  which  the  factors  0.169  and  0.2375  are  the  specific  heats  for 
air.  Applying  these  to  various  mixtures,  the  following  table 
results.  Col.  5  is  computed  from  the  formula 


COMPUTED  SPECIFIC  HEATS  OF  PRODUCTS  OF  COMBUSTION 
(GRASHOF  s  FORMULAS). 


I 

2 

3 

4 

5 

Propo-tion 
of  Air 
to  Gas  by 

Specific  Heat 

of  Mixture 
at  Constant 

Specific  Heat 
of  Mixture 
at  Constant 

Ratio 
Cj, 

Calculated 
Temperature 
Fahr.  of 

Volume. 

Vol.  6V 

Pressure  Cp 

Cv 

Combustion. 

4  to 

0.214 

0.289 

-35 

6010 

5 

0.206 

0.280 

-36 

6380 

6 

0.200 

0.273 

-36 

6300 

7 

o.  196 

0.268 

-37 

557° 

8 

0.193 

0.265 

-37 

5000 

9 

O.I9O 

0.262 

-37 

4580 

10 

O.T88 

o  259 

-.38 

4140 

ii 

0.186 

0.257 

-38 

3820 

12 

0.185 

0.256 

-38 

353° 

13 

0.184 

0-255 

-38 

3280 

14 

0.183 

0-254 

-39 

3090 

15 

0.182 

0.253 

-39 

2900 

The  second  method  is  to  analyze  the  products  of  combustion 
and  to  assume  that  the  effective  specific  heat  of  such  a  mixture  is 
the  sum  of  the  specific  heats  of  the  constituents.  Each  per- 
centage by  weight  of  the  constituent  gases  is  multiplied  by  the 
specific  heat  of  that  gas,  and  the  sum  of  these  products  is  called 
the  effective  or  rather  the  mean  specific  heat.  This  assumption 
may  or  may  not  be  correct. 

The  third  method  is  to  invert  the  use  of  the  theoretical  formula 
to  calculate  increase  of  temperature,  and,  by  observing  the  values 
of  the  variables  which  enter  into  it,  calculate  the  actual  value. 
That  is,  in  the  equation 


rp    rp J        ^y  _0_^ 

'    oc+y    CVe 


144  THE  GAS-ENGINE. 

let  both  T2  and  7\  be  temperatures  observed  in  an  actual  experi- 
ment, and  Q  the  heating  value  of  the  gas  in  B.T.U.,  while  y  is  the 
weight  of  fuel  in  the  mixture  and  x+y  the  total  weight  of  such 
mixture.  Then  Cve  is  the  only  unknown  factor.  If  this  method 
be  applied  to  CO,  for  example,  burning  to  CO2, 

rc+on    o    rcori 

Li2-hi6J~t~i6     L.44J 
CO        28     7 


O  +  CO     44     ii 

if  oxygen  were  the  supporter  of  combustion.     With  air,  how- 
ever, with  77  parts  of  nitrogen,  the  -r  of  supplied  oxygen  must 

be  multiplied  by  -  -  to  give  equivalent  air.     Hence 

100     16 
-X-£  =  2.5  Ibs.  air  nearly, 

23        2o 

so  that  the  mixture  will  be 

CO i       pound 

0 0.56     " 

N i  .94  pounds 


3-50 


made  up  of  1.56  pounds  of  CO2  and  1.94  pounds  of  N.    Hence 

12.  .7 

—  =  -  instead  of  —  . 


3-5     7 

For  CO  the  value  of  Q  is  about  10,000.    Then  if  the  range 
-7\  be  found  to  be 


2     10,000     10 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  145 

which  could  be  applied  for  other  cases  similar  to  the  typical  one. 
The  difficulty  here  is  the  inaccuracy  of  the  observations  of  T2  —  Tlt 
especially  in  engine  work,  where  the  changes  are  very  rapid  by 
conduction  of  the  cylinder-walls. 

A  fourth  basis  for  computing  the  effective  specific  heat  will 
be  by  measuring  the  increase  of  volume  in  a  combustion  at 
constant  pressure.  In  this  case  let  v2  be-  the  greater  volume  and 
Vj.  ,he  less.  Then  will 


since  at  constant  pressures  the  volume  will  be  directly  as  the 
absolute  temperatures.     But  it  is  also  true  that 

T       T  - 

J-  2—  -L  i  — 


hence,  by  dividing  by  7\  and  transposing, 

V-*=I*= 

vt     T,       + 
and  also,  by  multiplying  by  vly 


. 

But  since 

?L_X- 

T,     Pi 
it  will  be  true  that  the  volume  range 

R        yQ 

^ 


whence  the  actual  or  experimental  value  for  the  specific  heat 

c  _ 


146  THE  GAS-ENGINE. 

can  be  computed  if  plt  v2,  and  ^  be  observed  in  any  case,  and  R 
be  taken  at  its  value  53.35  for  air.  If,  for  example,  in  a  combus- 
tion at  atmospheric  pressure  a  pound  of  CO  burning  to  CO2 
gave  a  value  for  rv-i—rv^  of  40  cubic  feet,  then  the  computation  as 
in  the  preceding  example  would  give 

10,000 


A  fifth  method  by  analogy  would  be  a  similar  observation  or 
experiment  with  an  increase  of  pressure  caused  by  a  combustion 
at  constant  volume,  as  in  an  explosive  gas-engine.  Here  ob- 
viously the  above  equation  would  have  the  form 


If  the  pressure  range  in  a  closed  vessel  with  CO  burning  to 
CO2  be  observed  to  be  60  pounds  per  square  inch  when  the  vol- 
ume occupied  was  13  cubic  feet,  then 


10,000 


These  values  for  the  effective  specific  heat  deduced  from 
reliable  experiment  and  observation  are  so  much  higher  than 
the  accepted  accurate  determinations  by  the  physicists  for  prod- 
ucts of  combustion  or  for  air  as  to  confirm  the  general  deduction 
from  all  experiment  that  in  the  internal  heating  which  occurs 
in  a  gas-engine  the  theoretical  temperatures  called  for  with 
accepted  values  of  the  specific  heat  of  air  and  gas  are  not  attained 
in  practice.  The  reasons  which  are  most  probable  for  this 
phenomenon  have  been  already  foreshadowed  in  the  discussion 
of  the  volume  change  on  chemical  combination,  due  to  molecular 
rearrangement,  and  possibly  to  other  chemical  changes  which  may 
occur;  the  losses  in  dissociation  without  a  subsequent  complete 
combination  within  the  time  allotted  to  the  gas-engine  stroke;  the 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  347 

reaction  between  the  combining  gases  and  the  highly  conductive 
metal  walls  of  the  cylinder;  the  non-instantaneous  character 
of  the  combustion  with  imperfect  mechanical  mixtures  of  the 
components;  and  perhaps  also  a  varying  value  for  the  effective 
specific  heat,  being  greater  at  high  temperatures  than  at  the 
lower  ranges.  Internal  combustion  is  also  limited  in  heating 
effect  by  the  condition  that  the  fuel  cannot  combine  with  more 
oxygen  than  will  chemically  unite  with  it.  If  an  excess  of  oxygen 
or  air  is  present,  it  simply  increases  the  material  to  be  heated 
with  a  given  calorific  power  of  fuel,  and  not  only  does  not  increase 
the  intensity  of  the  heating,  but  lowers  the  resulting  temperature. 
Varying  composition  of  the  gaseous  mixture  due  to  governing 
or  high  speed  or  other  causes  affects,  therefore,  the  temperature 
in  the  cylinder.  With  external  heating  this  particular  limit  is 
not  set. 

56.  Value  of  the  Exponent  in  the  Equation  for  Expansion. 
—  When  a  mixture  of  gas  and  air  is  expanding  after  ignition, 
and  without  a  transfer  of  heat  from  without  to  replace  the  equiva- 
lent of  the  external  resistance  overcome,  the  expansion  is  called 
adiabatic  (par.  50),  and  the  equations  for  the  relations  of  pres- 
sures and  volumes  will  be  in  the  form 


In  the  gas-engine  the  exponent  n  is  not  unity,  but  is  the  ratio 
between  the  specific  heats  of  air  or  the  mixture  at  constant  pressure 
and  at  constant  volume  (par.  54).  But  the  preceding  treatment 
has  made  it  clear  that  neither  of  these  values  can  be  assumed  to 
be  those  resulting  from  laboratory  determinations  and  hence, 
of  course,  their  ratio  should  not  be  assumed.  To  do  so  is  to 
introduce  the  likelihood  of  several  serious  errors.  For  example, 
in  the  indicator-card  in  Fig.  22,  if 

v1  =  the  volume  of  the  clearance, 
7/2  =  the  final  or  terminal  volume, 
pQ  =  atmospheric  pressure  (14.7  Ibs.), 


148 


THE   G/tS-ENGINE. 


pu= pressure  at  compression  from  card, 
/  =  length  of  stroke,  feet  or  inches, 
x  =     "   -    "  clearance,  feet  or  inches, 


then  will 


which  becomes 


p 


* 


FIG.  22. 

from  which  the  third  unknown  can  be  calculated  if  the  two  others 
have  been  observed  or  the  value  of  n  is  assumed.     If  the  usual 

assumption  is  made  that  ^=1.41  or  -  =  .71   and  pv  be  observed, 

then  the  value  for  x  will  come  out  too  large,  and  computations 
for  the  temperature  after  ignition  from  the  formula 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR. 


149 


which  will  hold  when  the  volume  does  not  alter,  will  give  values 
for  Ti  which  are  too  large.  Hence  the  value  for  n  should  not 
be  assumed,  but  from  a  carefully  taken  indicator-card,  and  by 
careful  measurement  of  clearance  and  stroke  volumes,  the  ex- 
perimental or  effective  value  for  n  should  be  worked  out  for 
different  points  on  the  curves  of  both  the  expansion  and  com- 
pression lines.  In  an  actual  experiment,  for  example,  the  ex- 
pansion lay,  as  shown  in  Fig.  23,  between  the  upper  dotted  or 


FIG.  23 

isothermal  line  and  the  lower  dotted  or  adiabatic  line,  nearer  the 
latter  at  the  beginning.      If  values  for  both  p  and  v  be  taken  at 


various  pairs  of  points  in  the  stroke  as  indicated  in  Fig.  24,  the 
calculation  for  n  will  take  the  form 


J5°  THE  GAS-ENGINE. 

whence 


or 


In  the  experimental  case  referred  to,  the  values  of  n  from  the 
computations  based  on  the  diagram  came  out  i.io,  1.12,  1.13, 
1.14,  1.15,  1.  1  6,  with  an  average  of  1.14,  and  in  another  test  with 
an  average  of  1.20.  A  wider  range  of  generalization  has  shown 
that  the  ends  of  the  real  curves  and  some  intermediate  points  lie  on 
a  curve  whose  equations  are  for  compression  pv1-35  and  for  expan- 
sion^;1-4, equal  to  a  constant  (see  pars.  152,  202).  The  value 
for  n  will  often  be  slightly  higher  for  the  compression  curve  on  the 
diagram  than  for  the  expansion  curve.  Equality  of  value  on  the 
two  curves  may  be  tested  by  the  observation  whether  at  the  points 

P       P- 
p5  and  p4  on  the  compression  curve  the  ratio  is  true  that  —•  =^~- 

•L     3  JL    4 

For  let  x  be  the  exponent  for  the  expansion  curve,  and  y  the  ex- 
ponent on  compression,  then  p^v-ix=p.iv2x  will  hold  for  one,  and 
pz^iy=P^2y  f°r  the  other.  By  division, 


If  x  =  y  in  both  members, 


=  = 

pff  i&*9.     P.  P*' 

but  not  otherwise.  In  any  exhaustive  investigation  of  an  internal- 
combustion  engine  the  value  of  n  should  be  one  of  the  quantities 
to  be  computed  for  which  observations  should  be  made  (par.  174). 


ENERGY  DUE   TO  EXPANSION  OF  GAS  AND  AIR.  151 

57.  The  Continuous  Rotative  Motor  using  Pressure,  Im- 
pulse, or  Reaction. — The  treatment  in  the  foregoing  paragraphs 
of  th's  chapter  has  been  specially  directed  towards  a  statement 
of  the  phenomena  in  motors  of  the  piston  class.  The  operation 
of  media  whose  pressure  or  elastic  tension  is  affected  by  heat  is 
not  necessarily  restricted  to  motors  of  this  class.  A  design  of 
motor  similar  to  the  rotary  engine  in  steam-engine  practice  or 
similar  to  the  steam  turbine  can  be  made  available,  provided  a 
convenient  cycle  for  the  gas  can  be  secured  which  it  will  be  the 
purpose  of  the  next  chapters  to  discuss.  If  the  rotary-engine 
principle  is  sought  for,  it  will  require  to  receive  on  rotating  vanes 
the  pressure  from  the  expanding  gas,  and  the  difficulty  will  at  once 
be  met  of  securing  a  satisfactory  expansive  working  of  the  medium. 
It  is  much  more  likely  that  motors  of  the  turbine  class  which  utilize 
the  impulse  or  reaction  due  to  a  high  velocity  of  the  expanding  gas 
will  be  found  to  lie  in  the  direction  of  success  along  these  lines. 
The  problems  are  both  inherent  and  structural  when  air  with 
gas  is  used  as  the  medium,  by  reason  of  the  thermal  sluggishness 
of  the  hot  medium  acting  upon  the  vanes  or  plates  of  the  turbine 
and  the  difficulties  incident  to  working  with  the  high  temperatures 
required  by  air.  But  it  is  also  not  certain  at  the  present  state 
of  knowledge  that  the  jet-impact  method  of  working  a  motor 
would  give  an  economical  heat  transformation. 


CHAPTER  IV. 

THE  HEAT-ENGINE  CYCLE. 

58.  Introductory. — It  will  be  apparent  from  the  consider- 
ations in  the  foregoing  discussion  that  in  the  operation  of  gas- 
engines  of  the  piston  class  it  will  be  necessary  to  raise  the  con- 
dition of  intrinsic  energy  of  the  gas  at  the  beginning  of  the  work- 
ing stroke,  and  that  the  convenient  means  of  doing  this  is  by 
the  combustion  within  the  air  of  a  material  having  a  suitable 
calorific  power.  That  increased  condition  of  energy  makes  the 
gas  capable  of  doing  work  upon  the  head  of  the  piston  and  over- 
coming external  mechanical  resistance  by  its  expansion.  It  is 
desirable  at  the  end  of  the  expansion  that  this  mass  of  products 
of  combustion  and  air  shall  be  as  nearly  at  the  state  of  the  atmos- 
pheric air  surrounding  the  motor  with  respect  to  heat  and  avail- 
able energy  as  is  convenient  and  possible,  in  order  that  the  least 
amount  of  available  energy  may  be  thrown  away  and  wasted. 
That  expansion,  therefore,  should  be  accompanied  by  a  cooling 
or  lowering  of  temperature,  and  connected  therewith  a  reduction 
of  volume.  These  transformations  with  respect  to  the  internal 
energy  of  the  gas  will  be  recurrent  or  cyclic  in  their  action  and  will 
usually  repeat  themselves  in  a  fixed  order  of  succession.  A 
motor  of  the  class  in  question,  therefore,  is  said  to  have  a  " cycle" 
of  operations,  and  each  step  in  this  cycle  may  conveniently  be 
called  a  "phase."  The  extent  of  each  phase  and  the  period  of 
its  recurrence,  so  far  as  the  medium  is  concerned,  will  be  affected 
by  the  mechanical  appliances  whereby  this  succession  of  phases 
in  the  gas  or  medium  are  utilized  to  overcome  externaj  resistance. 


THE  HEAT-ENGINE  CYCLE.  153 

It  is  obvious,  therefore,  that  a  careful  distinction  should  be  made 
between  the  cycle  as  a  succession  of  phases  with  respect  to  heat 
energy  in  the  gas,  and  the  cycle  as  a  succession  of  events  deter- 
mined by  the  mechanical  construction  of  the  motor,  the  period- 
icity of  its*valve  action,  and  the  variation  in  the  supply  of  heat 
energy  from  variations  in  the  load,  etc.  This  distinction  be- 
tween the  two  types  of  cycle  is  believed  to  be  of  very  considerable 
importance  in  a  clear  analysis  of  the  operations  of  gas-engines.  • 

59.  The  Cycle  of  the  Steam-engine. — With  a  view  of 
making  clear  the  meaning  of  the  term  cycle  as  applied  to  the 
gas-engine,  it  may  be  convenient  to  refer  to  the  cycle  used  in 
the  steam-engine. 

The  media  for  heat-engine  purposes  may  be  roughly  divided 
(par.  5)  into  those  which  do  work  principally  by  utilizing  the 
expansion  which  occurs  when  it  changes  from  the  liquid  to  the 
gaseous  state  on  the  one  side,  and  on  the  other  those  that  utilize 
a  perfect  or  permanent  gas  whose  expansion  is  caused  by  the 
absorption  of  heat  (par.  7).  In  the  steam-engine  the  heat  is 
added  to  the  liquid  and  its  temperature  sufficiently  raised  so 
that  under  the  conditions  of  pressure  which  are  fixed  upon,  the 
liquid  becomes  a  gas.  In  the  second  stage  this  gas  is  allowed  to 
expand  to  as  low  a  pressure  as  possible  or  convenient,  doing  work 
upon  the  piston  by  such  expansion  in  the  engine.  The  gas 
is  then  discharged  either  as  a  gas  or  as  a  liquid.  This  cycle 
is  not  capable  of  being  modified,  except  in  minor  details.  It 
compels,  as  a  rule,  the  presence  of  three  essential  elements,  of 
which  one  shall  be  the  organ  concerned  with  the  production 
of  the  vapor;  the  second  shall  be  the  organ  for  the  utilization 
of  the  pressure  of  this  vapor,  and  the  third,  the  apparatus 
for  disposing  of  the  vapor  discharged.  In  condensing  steam- 
engines  this  latter  is  the  condenser,  and  in  non- condensing 
eng'nes  it  is  the  atmosphere.  The  amount  of  work  which  can 
be  done  with  a  given  amount  of  heat  in  a  prime  mover  of  this 
class  is  definitely  known,  within  certain  limits,  when  we  know 
how  much  liquid  can  be  converted  into  gas  by  a  given  amount 


154  THE  GAS-ENGINE. 

of  heat  and  the  relative  specific  volumes  of  the  liquid  and  result- 
ing gas.  The  chief  data,  therefore,  are  those  concerned  with  the 
properties  of  the  liquid  selected,  so  far  as  the  medium  is  con- 
cerned, and  the  motor  comes  in  only  to  affect  the  mechanical 
efficiency  of  the  system  for  the  conversion  of  heat  energy  into 
mechanical  energy.  With  the  perfect  or  permanent  gases  the 
range  of  possible  methods  of  heating,  expanding,  and  cooling 
becomes  greatly  enlarged  since  the  manner  of  heating,  the  method 
of  expansion,  and  the  ultimate  disposition  of  the  gas  after  the 
work  done  by  the  expanding  gas  and  the  properties  of  the  medium 
itself  are  without  significance.  This  peculiarity  was  first  pre- 
sented by  Carnot,  who  first  called  attention  to  the  existence  of 
the  cyclic  action. 

60.  The  Carnot  Cycle. — The  cycle  of  Carnot  may  serve  as  a 
type  for  all  cyclic  actions  with  a  permanent  gas.  The  four 
phases  of  the  cycle  are  represented  by  the  diagram  upon  the 
PV  plane  in  Fig.  25.  It  presents  a  cylinder  in  which  fits  a  piston, 
both  of  material  such  that  neither  have  any  capacity  for  heat, 
nor  do  they  offer  any  friction.  All  heat  received  is  to  be  utilized 
in  the  gas  which  is  acting  in  that  cylinder.  The  end  of  the 
cylinder  is  supposed  to  be  of  a  material  with  perfect  conductivity, 
so  that  the  gas  may  be  affected  as  to  its  heat  condition  without 
loss  from  the  process  of  transfer.  The  element  A  is  a  source 
of  heat  having  a  great  capacity,  so  that  all  the  heat  required  for 
the  cycle  can  be  transmitted  to  the  gas  at  the  maximum  tempera- 
ture, which  is  the  condition  of  maximum  efficiency  of  such  transfer 
and  is  maintained  at  the  temperature  7\.  The  element  C  is  a 
condenser  also  of  great  capacity  and  maintained  at  the  lowest 
available  temperature  T2,  so  that  the  cooling  of  the  gas  for  re^ 
duction  of  temperature  shall  be  done  with  the  maximum  effi^ 
ciency  of  that  process.  By  having  both  the  heater  and  cooler 
of  great  capacity,  no  change  in  7\  nor  T2  occurs  during  the  cycle. 
The  cover  B  of  a  non-conducting  material,  to  be  used  during  the 
period  of  expansion  and  compression,  is  applied  to  the  cylinder 
when  it  is  in  contact  with  neither  the  source  of  heat  nor  the  cooling 


THE  HEAT-ENGINE   CYCLE. 


155 


apparatus.  The  relations  of  pressure  and  volume  for  the  various 
stages  are  given  by  the  subscripts  on  the  diagram.  The  specific 
heat  at  constant  pressure  will  be  denoted  by  CP,  and  the  ratio 


c 


between  the  initial  and  final  volumes  — -,  which  must  be  the  same 

vd 
i} 
as  the  ratio  —,  will  be  denoted  by  the  factor  r,  or  the  ratio  of  the 

a 

expansion. 

There  will  be  four  steps  or  stages : 

(a)  Apply  the  heater  A .     The  pressure  rises ;    the  unit  weight 
of  gas  expands  isothermally  at  Tr     The  heat  energy  taken  in  is 

J5Ti-Criliyp.|ogf9 

(see  par.  181). 

(b)  Heater  A  is  removed,  cover  B  is  applied,  and  the  piston 
moves  out  at  the  expense  of  the  gas  temperature,  until  the  tem- 
perature falls  to  T2  by  such  expansion  against  external  resistance. 

(c)  Take  away  cover  B  and  apply  cool  body  or  condenser 
C  at  T2.     No  change  will  take  place,  because  the  expansion  is 
complete,  unless  the  piston  be  pushed  back.     But  if  the  piston 
is  retracted,  the  smallest  tendency  to  an  increase  of  temperature 


*56  THE   GAS-ENGINE. 

above  T2  is  at  once  met  by  a  flow  of  energy  into  the  condenser. 
The  gas  changes  its  total  heat  energy  down  to  the  stage  represented 
by  r2,  and  the  amount  rejected  to  the  condenser  will  be  the 
difference  between  the  energy  at  7\  and  T2,  or 

H2  =  CT2  hyp.  log  r. 

(d)  Remove  the  condenser  C  and  replace  B  when  the  point  d 
is  reached.  The  piston  is  now  still  further  forced  in  and  back 
until  the  gas  has  its  initial  volume  va,  and  if  the  point  d  was 
rightly  chosen  it  has  also  the  temperature  7\  at  which  it  started, 
because  the  compression  has  been  adiabatic,  and  the  cycle  has 
been  completed.  For  the  relations  of  vb  and  vc  to  produce  the 
desired  final  temperature  T2 


or 

rv  *•  rr\ 

v  T 


according  as  the  location  of  b  or  d  is  desired  (par.  52). 

It  will  appear,  therefore,  that  the  Carnot  cycle  gives  an  external 
work  in  foot-pounds  which  will  be  778  times  the  difference  be- 
tween the  heat  rejected  and  the  heat  received  (par.  47),  or,  for 
the  complete  cycle, 

Work=  778C(7\  -  T2)  hyp.  log  r, 

which  is  778  times  the  area  included  in  the  diagram  of  curves 
(Fig.  25),  all  transfers  having  been  made  at  maximum  efficiency. 
The  operation  of  the  Carnot  cycle  is  proved  to  be  that  of 
maximum  efficiency  for  the  conditions  assumed  by  the  expedient 
of  imagining  the  cycle  to  be  operated  in  reverse  direction  by  a 
similar  heat-engine.  It  can  be  proved,  if  both  engines  operate 
within  the  same  limits  of  temperature,  7\  and  T2,  and  one  drives 
the  other  as  a  motor,  while  the  other  operates  as  a  heat-pump, 
that  such  a  combination  makes  both  cycles  reversible,  and  that 
rll  reversible  heat-engines  working  between  the  same  limits 
cf  temperature  are  equally  efficient  or  that  the  efficiency,  in 
the  thermodynamic  sense,  is  independent  of  the  specific  heat  or 


THE  HEAT-ENGINE   CYCLE.  157 

other  physical  properties  of  the  medium  used.  The  formula 
for  efficiency  discussed  in  paragraph  47  is  immediately  deducible 
from  the  operation  of  the  Carnot  cycle. 

6 1.  The  Cycle  of  the  Internal-combustion  Engine. — The 
Carnot  cycle  and  the  equation  for  its  condition  of  maximum 
efficiency  do  not  apply  to  the  internal-combustion  engine  if  the 
maximum  temperature  in  the  cycle  be  taken  as  the  temperature 
after  ignition  has  occurred.  It  is  only  true  where  the  maximum 
compression  temperature,  is  taken.  It  will  be  apparent  that 
by  abandoning  the  indirect  methods  which  are  assumed  in 
the  typical  Carnot  cycle  for  transferring  heat  to  the  gas  a 
much  wider  range  of  possible  cycles  is  opened  up.  In  the 
first  place,  the  heating  may  occur  without  a  previous  com- 
pression; in  the  second  place,  the  compression  may  be  adia- 
batic  and  the  heating  isometric  (par.  49-53);  m  tne  third 
place,  the  compression  may  be  adiabatic,  the  heating  iso- 
piestic;  in  the  fourth  place,  the  compression,  may  be  adiabatic 
and  the  heating  isothermal;  in  the  fifth  place,  the  compression 
may  be  adiabatic  and  the  heating  may  follow  any  law  not  re- 
ducible to  the  foregoing  standard  methods.  Each  of  these  may 
be  made  to  vary  again  by  the  method  followed  in  expansion  and 
in  cooling.  Finally,  the  heating  may  be  atmospheric  without 
compression  or  with  compression,  and  where  there  is  compression 
the  cooling  may  be  according  to  varying  forms  of  the  phase. 
The  following  table  presents  in  analytic  form  the  possible  cycles 
for  such  engines: 

It  will  be  a  matter  to  be  discussed  in  Chapter  XVII  which 
of  these  cycles  are  available  or  unavailable  and  which  of  them 
offer  the  probabilities  for  the  best  efficiency. 

It  will  also  suggest  itself  to  determine  the  effect-of  the  cycle, 
so  far  as  it  requires  a  larger  volume  of  gas  under  one  method  of 
working  than  to  do  the  same  work  in  another.  The  larger  volume 
,of  gas  makes  a  more  bulky  motor.  Some  cycles  will  operate 
under  higher  temperatures  than  others,  and  others  through 
wider  ranges  both  of  temperature  and  pressure. 


158 


THE  GAS-ENGINE. 
CLASSIFICATION  OF  CYCLES. 


' 

2. 

3. 

4- 

5- 

6. 

Cycle  No. 

Compression. 

Heating. 

Expansion. 

Cooling. 

Cooling. 

I 

Isometric 

Adiabatic 

Isopiestic 

I  A 

Isometric 

Isopiestic 

IB 

M 

it 

Isothermal 

I  C 

it 

(t 

it 

II 
II  A! 
II  A2 
II  B 
IIC 

Adiabatic 
« 

u 
tt 
(( 

Isometric 
« 

M 

« 
« 

Adiabatic 

tt 
u 

(C 

Isopiestic 

Isometric 
« 

Isothermal 
Isothermal 

Isopiestic 
Isopiestic 

III 
III  A 
III  B 

Adiabatic 
« 

Isopiestic 
« 

Adiabatic 

Isopiestic 
Isometric 
Isothermal 

Isopiestic 
« 

me 

« 

« 

" 

l< 

IV 
IV  A 
IV  B 

Adiabatic 

Isothermal 

Adiabatic 
tt 

(C 

Isopiestic 
Isometric 
Isothermal 

Isopiestic 
tt 

IV  C 

" 

tt 

(( 

tt 

V 
VA 
VB 

Adiabatic 

« 

1C 

Any  law 

<e 
<« 

Adiabatic 
« 

u 

Isopiestic 
Isometric 
Isothermal 

Isopiestic 
<( 

VC 
VI 

1C 

Atmospheric 

« 

Isometric 

Isothermal 

VII 
VIII 

Adiabatic 

Adiabatic 

Isopiestic 
Isothermal 

IX 

Adiabatic 

« 

" 

Isometric 

X 

" 

" 

Any  law 

A  consideration  of  the  relative  advantages  of  the  various  cycles 
must  be  postponed  until  after  a  consideration  of  the  mechanisms 
or  motors  which  they  operate. 

62.  The  Otto  Cycle  with  Heating  at  Constant  Volume. — 
There  were  several  forms  of  gas-engine  proposed  and  built 
previous  to  1876,  to  which  reference  will  be  made  in  the  historical 
appendix  (Chapter  XX),  but  in  that  year  Dr.  Otto  brought  out, 
in  Germany,  the  engine  which  he  designated  as  his  "Silent" 
gas-engine,  to  distinguish  it  from  his  earlier  and  more  noisy 
type.  The  Otto  cycle  was  first  suggested  in  a  French  patent  of 
1862,  by  Alphonse  Beau  de  Rochas.  He  advocated  the  advan- 


THE  HEAT-ENGINE  CYCLE 


159 


tages  of  a  previous  compression  of  the  combustible  mixture  of 
gas  and  air,  and  proposed  to  do  away  with  a  separate  com- 
pressing pump-cylinder  for  this  purpose  by  making  only  one 
stroke  in  four  to  be  the  working  stroke  in  a  single-acting  engine. 
The  Beau  de  Rochas  or  Otto  cycle  involves: 

1.  Aspiration  of  the  mixture  of  gas  and  air  in  proper  propor- 
tions during  an  outgoing  stroke  of  the  piston  (1-2  in  Fig.  26). 

2.  Compression  of  the  mixture  by  the  return  of  the  piston 
(2-3-4).     This  compression  fills  a  comparatively  large  clearance 
volume  behind  the  piston,  which  must  be  so  adjusted  to  the  dis- 
placement by  the  piston  that  there  shall  be  no  danger  of  such 


FIG.  26. 

elevation  of  temperature  from  the  compression  as  to  ignite  the 
mixture  as  the  result  of  compression  alone  (pars.  152,  202). 

3.  The  piston  being  at  or  near  its  inner  dead  point  (4),  the 
compressed  mixture  is  ignited  by  some  acceptable  and  reliable 
device  (Chapter  XI),  at  which  the  pressure  rises   at   once  (4-5) 
and  exerts  its  outward  effort  to  drive  the  piston  forward.     Ex- 
pansion is  followed  by  gradual  lowering  of  pressure  during  this 
working  stroke  (5-6-7).     This  heating  is  therefore  done  at  con- 
stant volume. 

4.  The  exhaust  opens  just  beyond  7  and  the  products  of  com- 
bustion are  discharged  into  the  open  air  through  the  exhaust- 


i6o 


THE  GAS-ENGINE. 


valve  by  the  return  of  the  piston  to  its  inner  dead-centre  (8-1). 
The  cycle  then  repeats  itself. 


FIG.  27. 


Phase  No.  i. 


Phase  No.  2 


FIG,  28. 


It  is  apparent  thai  a  heavy  fly-wheel  must  be  used  to  equalize 
the  motion  of  the  crank -shaft,  having  energy  enough  stored  in  it  by 


THE  HEAT-ENGINE  CYCLE. 


161 


the  working  stroke  to  overcome  the  resistance  during  the  time  of 
the  other  three  strokes,  and  cause  also  the  piston  to  perform  the 
acts  of  the  cycle  in  the  cylinder.  High  rotative  speed  is  therefore 
an  advantage.  Furthermore,  a  high  initial  pressure  and  tem- 
perature are  desired,  with  a  low  terminal  value  for  both,  so  as 
to  secure  a  high  mean  value.  Rapid  inflammation  is  therefore 
desired,  and  the  methods  of  ignition  become  important.  Fig.  26 
is  a  diagrammatic  analysis  of  the  succession  of  events,  while 
Fig.  27  is  the  normal  PV  diagram  from  an  actual  engine.  To 
connect  the  various  steps  of  the  motor  mechanism  with  the  effects 
in  the  cylinder  and  upon  the  gas  and  mixture,  the  diagrams  of 
Figs.  28  and  29  will  be  serviceable.  They  show  the  effect  of  the 


Phase  No.  3 


V 


Phase  No.  4. 

FIG.  29. 

successive  traverses  of  the  motor  piston,  generating  each  its 
appropriate  line  of  the  diagram  as  the  volume  varies  and  causes 
the  pressure  to  vary  with  it.  The  gradual  building  up  of  the 
typical  diagram  of  pressures  is  made  clear.  The  same  illustrations 


162 


THE   GAS-ENGINE. 


show  the  succession  of  operations  per- 
formed by  the  valves.  In  phase  No.  i  the 
gas  and  air  inlet  valves  are  open,  the  ex- 
haust is  closed ;  in  phases  No.  2  and  No.  3 
all  are  closed;  in  phase  No.  4  the  exhaust 
is  open,  and  the  others  are  closed.  The 
ignition  phenomenon  occurs  at  the  be- 
ginning of  phase  No.  3.  By  the  expedient 
of  plotting  the  observed  pressure  acting 
upon  the  crank-pin  at  each  point  of  the 
two  strokes  of  the  piston,  as  is  done  in 
Fig.  30,  the  values  of  the  varying  effort 
on  the  engine-shaft  appear  clearly  to  the 
eye.  It  is  obvious  that  in  this  design 
only  the  one  working  stroke  in  four 
traverses  of  the  piston  is  a  working  or 
effective  stroke. 

63.  The  Brayton  Cycle  with   Heating 
at    Constant   Pressure. — The  second  im- 
portant cycle  is,  historically,  a  little  earlier 
than  that   of  Otto.     Its  principle  is  the    g 
compression  of  a  mixture  of  inflammable    t 
gas  and  air  'which  is  introduced  into  the    ^ 
working  cylinder  and  there  ignited  so  as    < 
to  burn  in  such  a  manner  that  the  pres-    o 
sure  shall  not  increase  above  a  fixed  con-    o 
stant  value.     The  power  is  generated  by    § 
the  increase  of  volume  at  constant  pres-    § 
sure  due  to  the  inflammation  of  the  gas    5 
in    the    air.     Such    engines    are    not    ex-    J 
plosive,  but  the  pressure  increases  gradu-    z 
ally,  due  to  slow  combustion.     The  credit    J 
for  using  this  cycle  attaches  to  a  Phila- 
delphian    named    Brayton,    who    utilized 
it  in  an  engine  in   1873    (see  Fig.   218). 
In  England  Messrs.  Simon  used  the  same 


01 


1 


THE  HE/IT-ENGINE   CYCLE.  163 

cycle  in  1878.     Credit  is  also  due  to  Sir  William  Siemens,  who 
proposed  the  cycle  as  far  back  as  1860,  but  no  engine  was  built. 

In  the  constant-pressure  cycle  there  are  usually  two  cylinders, 
one  a  compressing -pump  and  the  other  the  working  cylinder.  The 
charge  of  gas  and  air  is  drawn  into  the  pump  and  compressed 
on  the  return  of  the  piston  into  a  receiver.  The  pressure  in  the 
receiver  may  be  about  60  or  80  pounds.  The  mixture  flows 
from  the  receiver  into  the  working  cylinder  and  is  ignited  as  it 
enters,  receiving,  therefore,  a  supply  of  hot  mixture  at  constant 
pressure  until  the  valve  cuts  off  admission.  From  the  point  of 
cut-off  to  the  end  of  the  stroke  the  volume  of  gases  is  expand- 
ing, and  of  course  the  terminal  pressure  can  be  reduced  by  ad- 
justing the  point  of  cut-off.  The  work  diagram  on  the  PV  plane 
from  such  a  cycle  is  quite  similar  to  that  of  the  steam-engine. 

64.  The    Cycle    with   Heating   at    Constant   Temperature. — 
The  third  variable  in  the  pressure-volume-temperature  series  is 
the  temperature,  and  a  cycle  in  which  the  addition  of  the  heat  to 
the  mixture  should  be  made  at  a  constant  temperature  would  con- 
stitute a  third  class.     The  nearest  actual  approach  to  this  cycle 
is  in  that  which  is  made  use  of  in  the  Diesel  engine.     In  this  cycle 
the  air  is  drawn  in  on  the  aspirating  phase  of  the  cycle  and  is 
compressed  by  the  energy  in  the  fly-wheel  to  a  high  pressure. 
It  is  usually  about  500  pounds  in  small  sizes.     Into  this  highly 
compressed  and  heated  air  is  introduced  the  jet  of  combustible. 
At  first  proposed  by  Diesel,  this  combustible  was  kerosene  oil, 
and  it  was  supposed  to  be  completely  ignited  by  the  high  tem- 
perature  of  the  air,  so  that  the  air  should  receive  all  its  heat 
energy  at  the  temperature  prevalent  when  the  ignition  was  begun. 
It  is  more  than  questionable,  in  view  of  the  time  necessary  to 
ignite  the  oil  and  to  heat  the  air,  whether  this  heating  of  the  air 
is  done  at  a  constant  temperature  throughout  its  entire  mass 
in  actual  practice.     To  the  extent  to  which  this  result  is  attained 
the  cycle  approaches  the  Carnot  cycle,  in  which  the  heating  is 
supposed  to  be  at  constant  temperature. 

65.  Advantages    of     the    Internal-combustion    Principle. — 


1^4  THE  GAS-ENGINE. 

In  discussing  the  advantages  of  the  internal-combustion  prin- 
ciple as  a  means  of  deriving  mechanical  energy  from  liberation  of 
heat,  it  is  unavoidable  that  the  comparison  be  made  between  this 
principle  and  that  of  the  ordinary  steam-engine.  In  the  latter 
there  has  to  be  the  furnace  and  the  boiler,  exterior  to  the  engine 
proper,  both  for  liberation  of  heat  and  for  storage  of  that  liberated 
energy.  There  should  therefore  be  a  distinction  drawn  between 
the  advantages  due  to  the  use  of  liquid  or  gaseous  fuels,  which  are 
practically  essential  in  the  internal-combustion  engine,  and  those 
which  belong  to  the  direct  utilization  of  the  energy  of  the  fuel  by 
combustion  in  the  cylinder,  instead  of  outside  of  it,  in  a  furnace. 
Hence  the  advantages  of  the  direct  internal  combustion  are: 

(1)  The  energy  of  the  heat  liberated  by  combustion  operates 
directly  upon  the  piston  to  produce  motion,  and  without  inter- 
vening appliances. 

(2)  The  economy  in  fuel  per  horse-power  per  hour  is  greater 
than   with  steam  or  externally  heated   air,  because   heat  is  not 
wasted  in  furnace  or  chimney,  or  in  doing  work  upon  a  trans- 
ferring medium  which  is  not  utilized  in  the  engine. 

(3)  No   fuel   is   consumed   wastefully   in   getting   the   motor 
ready  to  start,  nor  is  any  wasted  in  the  furnace  after  the  engine 
stops.      The  losses  in  banking  fires  under  boilers  which  are  run 
intermittently  are  avoided,  the  losses  due  to  blowing  steam  to 
waste  through  safety-valves  when  the  motor  is  stopped  for  short 
periods,  and  the  losses  of  fuel  through  the  grates  from  cleaning 
and  when  the  run  is  over. 

(4)  The  radiation  losses  of  heat  from  the  boiler-setting  or 
furnace  do  not  occur. 

(5)  The  bulk  and  weight  of  the  boiler  and  its  setting  are 
eliminated,  as  well  as  their  cost. 

(6)  This  gives  this  type  of  motor  a  distinctly  portable  char- 
acter if  desired,  even  up  to  considerable  sizes,  where  it  may  be 
convenient  to  have  the  motor  follow  to  the  place  where  the  work 
is  to  be  done,  as  in  logging  and  lumbering. 

(7)  The  absence  of  boiler  and  chimney  eliminates  the  repair 


THE  HEAT-ENGINE  CYCLE.  165 

and  maintenance  account  attaching  to  them,  as  well  as  the  labor 
to  operate  them  and  their  first  cost. 

(8)  The  absence  of  the  boiler  and  its  furnace  lowers  the  in- 
surance risk  (unless  offset  by  the  presence  of  the  producer,  the 
gas-holder,  or  the  stored  liquid  fuel). 

(9)  The  absence  of  the  boiler  avoids  a  necessity  for  licensed 
operators  which  are  required  both  afloat  and  ashore  where  steam- 
plants  are  run. 

(10)  The  motor  is  ready  to  start  on  the  instant  and  without 
previous  preparation  or  delay  from  starting  a  fire  and  getting 
up  pressure. 

(n)  When  the  fuel-supply  is  shut  off,  the  motor  stops  and 
there  is  no  attention  which  the  plant  requires  gradually  to  shut 
it  down.  These  two  latter  considerations  are  particularly  potent 
with  respect  to  the  automobile  uses  of  these  motors. 

(12)  This  principle  lends  itself  easily  to  the  condition  where 
storage  of  energy  is  required.     With  gas-burning  engines,   the 
producer  may  be  run  at   high  efficiency  when   convenient,  and 
the  gas  held  in  gas-holders  till  needed,  or  the  energy  in  liquid 
fuel  may  be  drawn  into  the  motor  through  carburetors  (Chap.  X) 
as  required.     This  is  convenient,  for  instance,  where  a  plant  is 
to  be  worked  overtime. 

(13)  Incident  to  this  is  the  advantage  of  subdividing  power 
units  in  a  large  plant.     Each  motor  may  receive  its  supply  of 
motor  energy  through  pipes  as  gas  without  loss,  or  from  fuel 
tanks,  and  such  motors  can  be  run  independently  of  each  other 
as  to  capacity,  speed,  time,  and  the  like,  as  long  as  the  store  oi 
gas  or  oil  holds  out. 

(14)  In   compressed    gas    in   tanks   under  pressure   a   large 
amount  of  fuel  energy  and  power  may  be  stored  in  small  bulk 
and  weight,  to  be  expended  through  reducing-valves  to  motors 
as  required.      This  property  is   only  of  moment  when  the  fuel 
weight  must  be  reduced  as  in  aerodromes.     In  automobile  and 
yacht  practice  the  liquid  fuel  does  not  weigh  enough  to  make 
gaseous  compression  worth  while. 


166  THE  GAS-ENGINE. 

(15)  The   rapidity   with    which   flame   propagates   itself    in 
an  explosive  mixture  of  fuel  and  air   renders    a    high    number 
of  rotations  of  the  shaft  possible  per  minute.      This  makes  a 
high-speed   multi- cylinder   engine   of   small    weight   per    horse- 
power. 

(16)  The  rapid  ignition  of  explosive  mixtures  gives  a  high 
initial  pressure  at  the  beginning  of  a  piston-stroke.     Where  this 
means  also  a  high  mean  pressure  it  gives  a  powerful  engine  for 
a  given  cylinder  volume. 

(17)  There  is  no  storage  of  large  amounts  of  energy  in  the 
form  of  pressure  in  a  containing  vessel,  a  rupture  of  which  will 
cause  disaster. 

(18)  There  is  no  boiler  to  give  difficulties  with  a  water  con- 
taining salts  in  solution,  and  requiring  a  constant  watchfulness 
to  keep  properly  supplied  with  water  lest  an  accident  result  from 
low  water  and  an  overheated  boiler. 

(19)  There    is   no    exposed  flame   or  incandescent  fuel-bed 
requiring   care   and   watchfulness.     Such  flames   in   absence   of 
good  draft  arrangements  may  blow  back  or  downwards  in  gusts 
of  wind  outdoors,  and  are  sources  of  danger  in  accidents,  if  they 
can  reach  the  fuel- supply. 

(20)  The  mechanism  of  the  motor  is  simple  in  principle  and 
does  not  involve  a  great  number  of  parts  in  motion. 

The  gas-   or  oil-engine,   furthermore,   attaches  to  itself  the 
advantages  of  gas-firing  and  mechanical  stoking,  in  that 

(21)  The  normal  and  proper  combustion  is  smokeless; 

(22)  The  fuel  does  not  require  so  great  a  diluting  excess  of  air 
for  combustion,  which  lowers  the  temperature  of  the  latter; 

(23)  The  avoidance  of  dust,  sparks,  or  ashes; 

(24)  The  liquid  or  gaseous  fuel  will  be  handled  mechanic- 
ally  by   pumps   or  pressure  organs  into  the  motor  apparatus. 
Hence  the  labor  and  cost  of  such  handling  are  avoided,  and  the 
cost  of  removal  of  ashes. 

It  should  not  be  forgotten  in  a  study  of  the  foregoing  that 
in  cities  where  gas  is  made  at  central  stations  and  distributed 


THE  HEAT-ENGINE  CYCLE.  167 

by  mains  the  central  generating  plant  has  had  to  assume  many 
of  the  disadvantages  whose  avoidance  constitutes  the  arguments 
for  the  internal- combustion  motor.  If  the  motor  operates  its 
own  producer,  as  an  isolated  gas-making  plant,  some  of  the  above 
arguments  disappear.  If  the  motor  uses  liquid  fuel,  as  in  the 
automobile,  then  all  of  the  arguments  hold  whjsh  apply  to  this 
form  of  motor. 

66.  Disadvantages  of  the  Internal-combustion  Principle. — 
On  the  other  hand,  there  are  certain  arguments  against  the 
internal -combustion  motor  as  now  in  use,  some  of  which  are 
inherent,  and  others  of  which  attach  more  to  some  types  than, 
to  others. 

.  (i)  The  Otto  cycle  (pars.  62  and  69)  gives  only  one  working 
stroke  in  four  piston-traverses.  In  the  two-phase  cycle  (par.  73) 
there  is  one  working  stroke  in  two  traverses.  For  a  given  mean 
pressure  the  cylinder  volume  of  the  gas-engine  will  be  larger  than 
in  the  double-acting  steam-cylinder  at  the  same  speed. 

(2)  In   single-cylinder  engines  the   crank  effort   is   irregular 
(par.  62);    hence  a  heavy  fly-wheel  is  required  for  steadiness,  or, 
a  number  of  cylinders  correcting  the  unsteadiness  adds  weight  to 
the  engine. 

(3)  The  motor  does  not  start  from  rest  by  the  simple  motion 
of  a  lever  or  valve.     It  has  to  be  started  by  an  auxiliary  apparatus 
in  which  the  energy  required  to  start  it  has  been  previously  stored 
(par.  164)  or  which  may  develop  enough  energy  to  cause  one  work- 
ing stroke  to  be  made. 

(4)  This  entails  a  clutch  or  other  transmission  mechanism 
between  the  motor  cylinder  and  the  useful  resistance,  so  that 
auxiliary  starting  shall  not  involve  overcoming  the  total  external 
resistance  also. 

(5)  There  is  no  way  of  increasing  the  power  of  the  engine 
beyond  a  limit  set  by  the  cylinder  diameter  to  meet  short  demands 
for  a  greater  effort  than  the  normal,  except  by  running  normally 
at  less  than  the  full  load. 

(6)  There  is  no  way  in  Otto  engines  to  increase  the  period 
during   which   the    predetermined   maximum    pressure    may    be 


1 68  THE  GAS  ENGINE. 

exerted  on  the  piston.     As  soon  as  the  piston  begins  to  make 
its  stroke,  the  pressure  begins  to  fall  off  at  once 

(7)  There  is  no  storage  of  energy  except  in  the  living  force 
of  the  fly-wheel  to  be  drawn  upon  for  such  temporary  emergency 
of  overload.     The  mass  of  hot  water  in  the  boiler,  or  the  accu- 
mulation of  pressure  in  it,  is  such  a  reservoir  in  the  other  systems. 

(8)  The  inconvenient  heat  of  the  combustion  in  the  cylinder 
makes  it  necessary  to  use  some  system  for  cooling  the  metal  of 
walls  and  valve-chambers,  to  prevent  distortion  and  rapid  oxida- 
tion.    In  small  cylinders  this  cooling  may  be  done  by  air;   with 
larger  motors  where  the  quantity  of  heat  in  question  is  greater 
this  cooling  will  be  best  done  by  circulation  of  water.      This 
weight  or  volume  of  water  and  the  apparatus  to  circulate  it  are 
an  objection. 

(9)  The  water  in   cooling   jackets    enveloping   the   cylinder 
carries  off  heat  unutilized. 

(10)  The  cooling  wafcir  lowers  the  mean  pressure. 

(n)  In  spite  of  cooling  water  the  valves  become  leaky  and 
require  attention  and  renewals. 

(12)  It  is  difficult  to  secure  a  low  final  temperature  when  the 
exhaust  opens.     Hence  a  considerable  pressure  exists  just  when 
the  valve  releases  the  cylinder  contents,  and  the  escape  of  these 
high-pressure   products   of   combustion   into   the   air   and   their 
expansion  on  their  escape  causes  a  disagreeable   coughing  or 
barking  noise. 

(13)  The  high  temperature  of  the  cylinder  makes  lubrication 
difficult  and  uncertain. 

(14)  If  combustion  is  not  complete  in  the  cylinder,  the  odor 
of  the  .exhaust  is  offensive. 

(15)  If  rates  of  propagation  of  the  flame  are  not  adjusted  to 
the  speed,  or  if  explosive  charges  pass  unignited  into  the  exhaust 
passages  or  pipes,  there  may  occur  explosions  of  some  violence 
in  these  passages  or  pipes,  with  their  attendant  noise  and  alarm- 
ing shock.     In  many  cities  the  fire  laws  compel  the  exhaust-pipes 
from  gas-engines  to  be  caried  in  pressure- resisting  metal  pipes 


THE  HEAT-ENGINE   CYCLE.  169 

completely  to  the  free  air,  and  do  not  permit  them  to  be  simply 
introduced  into  brick  chimney-flues. 

(16)  Imperfect   combustion  also  results  in  deposits  of  lamp- 
black or  soot,  which  clog  or  cake  upon  the  working  parts  and  are 
not  only  defiling  but    presently  stop   their    working.      Ignition 
apparatus  is  particularly  liable  to  this  trouble. 

(17)  The   high   initial   pressure   in   the   cylinder  due   to   the 
ignition  produces  a  jar  or  vibration. 

(18)  Governing  is  not  easy,  since  it  must  effect  a  phenomenon 
which  is  nearly  instantaneous  in  its  duration.     When  the  work 
of  the  engine  is  variable,  governing  may  not  be  close. 

(19)  If  the  compression  is  defective  or  badly  adjusted,  the 
power  of  the  engine  suffers. 

(20)  If.  the  ignition  apparatus  is  defective  or  out  of  commis- 
sion, the  motor  stops  dead. 

(21)  If  the  carburetor  is  out  of  adjustment,  the  motor  slows 
down  gradually  and  stops. 

(22)  The  motor  does  not  usually  run  in  both  directions,  and 
reversing  therefore  requires  a  train  of  gear  to  reverse  the  applica- 
tion of  power.     Such  gears  are  apt  to  be  noisy. 

(23)  The  normal  motor  runs  at  its  maximum  efficiency  only 
when  running  at  a  fixed  speed.     To  get  varying  speeds,  either  the 
reversing  train  may  be  made  a  variable- speed  train  (with  attendant 
noise  and  difficulty  in  shifting  speed  when  motor  and  resistance 
are  both  moving),  or  the  speed   may  be  varied  by  making  the 
power  of  the  cylinder  vary  by  throttling  the  mixture.     This  latter 
will  usually  be  attended  with  loss  of  efficiency;   and  when  carried 
to  a  limit  of  speed,  the  motor  will  cease  to  operate  its  cycle  and 
will  stop. 

All  of  this  last  group  of  disadvantages  are  the  result  of  the  one 
peculiarity  of  the  internal- combustion  motor  that  it  generates 
the  power  for  each  independent  stroke  at  the  beginning  of  that 
stroke,  and  has  no  reservoir  of  stored  energy  behind  it.  Hence 
anything  which  attacks  the  reliable  action  of  the  processes  which 
culminate  in  each  single  stroke  will  stop  the  motor.  This  has 


17°  THE  GAS-ENGINE. 

given  an  unreliab  lity  or  tricky  character  to  many  forms  of  motor 
when  the  real  difficulty  was  the  crudity  of  the  apparatus  which 
was  used  to  conduct  the  processes.  Hence  the  importance  of 
the  subsequent  chapters,  treating  on  governing,  ignition,  carbura- 
tion,  and  manipulation,  in  which  these  detailed  processes  receive 
fuller  treatment. 

67.  Variations  in  Cycle. — It  will  be  apparent  from  a  con- 
sideration of  the  table  in  paragraph  61  that  minor  variations  in 
cycle  will  be  caused  by  the  effects  of  the  appliances  for  governing, 
in  so  far  as  these  operate  to  vary  the  initial  and  final  temperatures 
of  the  expanding  mixture.  Where  the  exhaust-valve  of  the 
engine,  for  example,  opens  before  the  expansion  is  complete, 
there  will  be  a  drop  in  pressure,  resulting  from  the  free  expansion 
in  the  air  without  doing  work.  This  free  expansion  will  be  the 
occasion  of  two  steps  in  the  cooling  process  as  indicated  in  the 
table,  and  this  action  is  the  occasion  for  some  of  the  differentia- 
tions in  cycles  of  the  several  groups.  The  cycles  which  involve 
heating  at  atmospheric  pressure  compel  the  use  of  an  engine  of 
such  bulky  cylinder  volume  that  it  is  scarcely  necessary  to  give 
consideration  to  them. 


CHAPTER  V. 

GAS-ENGINES  BURNING  GAS. 

68.  Introductory. — Referring  to  the  distinction  drawn  litre 
tofore  between  the  cycle  used  in  any  engine  and  the  mechanisnv 
which  is  designed  to  utilize  that  cycle,  the  present  chapter  pre- 
sents, briefly,  the  development  of  the  modern  engine  using  gas. 
The  engine  using  gas  as  a  source  of  heat  is,  historically,  older 
than  that  using  the  liquid  fuels.     The  tvpes  chosen  to  present 
the  engines  which  have  utilized  the  cycles  treated  in  the  previous 
chapter  are  five  in  number. 

69.  The    Otto    Engine. — The    Otto    Silent   engine  of   1876, 
and  as  since  modified,  closely  resembles  a  single-acting  steam- 
engine.     The  cylinder  is  somewhat  longer  than  required  by  the 
stroke  as  limited  by  the  crank,  in  order  that  between  the  head  of 
the  piston  and  the  head  of  the  cylinder  on  the  dead-centre  may 
be  a  volume  of  sufficient  extent  (C)  to  contain  the  mass  of  com- 
pressed gas  and  air  which  is  required  for  the  working  stroke 
(pars.  152,  202).     In  the  usual  forms  of  the  European  stationary 
Otto  engine  the  cylinder  is  horizontal.     In  it  fits  a  long  trunk 
piston,  B.     The  trunk  construction  gives  a  considerable  contact 
area  to  guide  the  piston  in  its  traverse  of  the  cylinder,  and  the 
piston  itself  is  of  the  box  construction,  so  that  the  working  face 
may  be  kept  at  a  considerable  distance  from  the  pin  on  which  the 
connecting-rod  swings.     The  cylinder  is  water- jacketed  in  order 
that  it  may  be  kept  cool  enough  to  avoid  deformations  and  to  keep 
the  valves  tight  and  to  permit  of  effective  lubrication.      (Fig.  31.) 

The  valves  which  are  needed  for  the  Otto  cycle  are  an  inlet- 

171 


172 


THE  GAS-ENGINE. 


valve  for  gas  and  an  inlet- valve  for  air  (Figs.  28  and  29), 
which  shall  be  opened  upon  the  aspirating  outgoing  stroke  of 
the  piston.  These  valves  are  so  proportioned  as  to  give  the 
proper  mixture  of  gas  and  air  when  the  valves  are  opened.  .  On 
the  side  of  the  cylinder  opposite  the  inlet  openings  in  the  designs 
copied  after  Fig.  31  is  the  exhaust- valve,  which  is  usually  a 
lifting-  or  poppet-valve  similar  to  the  gas-inlet  valve.  This 
exhaust- valve  opens  on  the  return  stroke  after  the  working  stroke, 
and  is  to  allow  the  products  of  combustion  to  escape  freely  to  the 


FIG.  31. 

outer  air.  In  addition,  the  mechanism  of  the  engine  must  pro- 
vide for  the  ignition,  properly  timed,  of  the  mixture  which  has 
been  compressed  in  the  clearance  space  behind  the  piston.  In 
the  early  form  of  the  Otto  engine  this  ignition  was  effected  by 
the  large  slide-valve  M  operating  across  the  end  of  the  cylinder. 
This  valve  was  held  against  the  head  of  the  cylinder  by  a  cover- 
plate  N  and  strong  spiral  springs.  The  slide-valve  design  of 
Fig.  31  limited  the  speed  or  number  of  revolutions  per  minute 
which  the  engine  could  make,  and  the  problem  of  its  proper 
lubrication  was  always  a  difficult  one.  The  inlet-  and  exhaust- 
valves  and  this  sliding  ignition  and  timing  valve  were  operated 
from  a  lateral  shaft  P  at  the  side  of  the  cylinder,  driven  by  a  pair 
of  gears  from  the  main-  or  crank-shaft.  The  diameters  of  these 


GAS-ENGINES   BURNING    GAS  173 

bevelled  gears  were  so  adjusted  that  the  valve-  or  lay-  or  cam- 
shaft made  one  revolution  while  the  main-shaft  made  two.  This 
made  it  possible  for  the  valve-shaft  to  time  the  actions  of  its  cams 
so  that  they  would  come  once  in  each  two  revolutions  of  the  main- 
shaft,  as  is  the  requirement  of  the  Otto  cycle.  The  lateral  shaft 
also  drives  the  governing  appliance  and  is  a  convenient  attach- 
ment for  devices  to  secure  mechanical  oiling.  The  feature  of  the 
governing  of  the  Otto  engine  will  be  referred  to  in  a  subsequent 
chapter,  but  in  brief  ihe  governor  acted  upon  the  gas- valve  to  open 
it  more  or  less,  or  not  to  open  it  at  all,  while  without  action  upon 
the  air-inlet  valve.  The  effect  of  this  action  was  to  impoverish, 
the  mixture  when  the  gas- valve  was  partly  opened,  and  to  admit- 
no  combustible  whatever  when  the  gas- valve  was  not  open  at  all. 

The  subject  of  ignition  also  will  be  treated  separately,  but 
in  the  older  standard  form  the  transverse  slide-valve,  after  closing 
the  admission  from  the  gas-  and  air-passages,  presents  a  cavity 
in  its  face  which  is  filled  with  flame  from  an  exterior  flame  at  T 
which  is  burning  in  the  open  air.  This  flaming  cavity  L  in  the 
valve  is,  by  its  motion,  cut  off  from  connection  with  the  outer 
air  just  before  it  is  put  into  connection  with  the  explosion- 
port,  /,  filled  with  compressed  mixture.  Through  this  explosion^ 
port  which  communicates  with  the  clearance  volume,  the  charge 
is  ignited  before  the  piston  has  made  any  considerable  move-; 
ment  from  its  dead-centre. 

It  will  be  apparent,  from  this  description,  that  the  engine  in 
carrying  out  the  cycle  makes  one  working  stroke  in  two  complete 
revolutions  of  the  fly-wheel  shaft,  and  that  each  stroke  of  the 
piston  represents  one  phase  of  the  cycle.  The  fly-wheel  must, 
therefore,  be  massive,  in  order  that  during  the  three  auxiliary 
strokes  (Fig.  30)  it  may  have  stored  up  energy  from  the  one 
working  stroke  to  overcome  the  resistance  external  to  the  engine 
and  to  perform  the  functions  of  the  cycle.  It  is  obvious,  further- 
more, that  the  engine  must  be  started  so  as  to  produce  one  com- 
pression and  an  ignition  before  it  will  begin  to  revolve;  by  its  own 
motor  energy.  The  engine  will  usually  stop,  in  the  case  of  a 


174  THE   GAS-ENGINE. 

single-cylinder  motor,  with  the  compression  partly  begun,  but 
not  completed.  The  advantage  of  several  cylinders  operating 
on  one  crank-shaft  is  apparent  when  this  peculiarity  of  the  Otto 
cycle  and  the  Otto  engine  is  concerned.  It  is  very  usual  to  have 
a  lever  whereby  a  special  cam  can  be  thrown  into  action  upon  the 
exhaust-valve,  so  that  in  large  engines  the  very  great  effort  to 
start  the  engine  may  be  diminished  by  allowing  some  of  the  com- 
pression behind  the  piston  to  be  relieved  into  the  exhaust  until 
the  first  revolution  or  two  shall  have  been  made. 

The  more  modern  forms  of  the  Otto  engine  use  poppet- 
valves  and  an  electric  ignition  for  the  firing  of  the  compressed 
mixture  behind  the  piston.  Of  course  any  of  the  systems  described 
in  the  chapter  on  ignition  may  be  applied  to  the  Otto  cycle. 

The  Clerk  engine  (Fig.  32)  was  designed  along  the  lines  of 
the  Otto  engine  and  to  use  its  cycle,  while  securing  an  impulse 
from  the  ignition  of  a  compressed  charge  at  every  revolution  of 
the  main- shaft.  This  engine  was  introduced  about  1880.  It 
contains  two  cylinders,  of  which  one  is  a  charging  or  displacing 
cylinder  which  draws  in  the  combustible  charge  and  transfers 
it  directly  or  through  a  receiver  to  the  other,  which  is  the  power 
or  motor  cylinder.  The  displacer  crank  is  90°  in  advance  of  the 
motor  crank.  The  displacer  cylinder  and  receiver  volume  trans- 
fer the  charge  into  the  clearance  space  behind  the  motor  cylinder, 
where  it  is  compressed  by  the  return  stroke  of  the  piston.  The 
exhaust-ports  EEf  of  the  motor  cylinder  are  formed  in  the  side 
of  its  bore  at  a  point  such  that  as  the  piston  reaches  the  outer 
dead-centre  it  shall  have  uncovered  these  ports  so  as  to  allow 
the  products  of  combustion  to  escape  into  the  exhaust-pipe  and 
so  to  the  open  air.  The  displacer  piston  sends  its  charge  into  the 
clearance  volume  at  the  back  end  so  as  to  act  somewhat  to  sweep 
the  products  of  combustion  from  the  preceding  stroke  before 
them  into  the  exhaust-openings.  Compression  resistance  in 
starting  can  be  relieved  by  a  by-pass  into  the  exhaust. 

A  modification  of  the  Otto  and  Clerk  engine  using  the  same 
cycle  is  to  close  the  crank  end  of  the  cylinder  and  so  arrange  the 


GAS-ENGINES  BURNING   GAS. 


175 


valves  that  the  front  or  crank  end  of  the  piston  shall  discharge 
the  functions  of  the  displacer  piston  of  the  Clerk  engine.  By 
this  means,  the  engine,  as  in  the  Clerk  engine,  gives  one  impulse 


FIG.  32. 

or  working  stroke  in  every  revolution  of  the  crank-shaft.     Such 
engines  are  called  "  two-cycle"  engines  (par.  73). 

70.  The  Nash  Engine. — The  Nash  engine  is  an  American 
design  using  two  or  more  vertical  cylinders  each  operating  upon 
the  Otto  cycle  (Fig.  33).  By  using  two  cylinders  side  by  side, 
there  will  be  two  working  strokes  in  two  revolutions,  which  tend 
to  give  a  more  equal  turning  movement  to  the  fly-wheel  shaft. 
The  inlet-valves  for  gas  and  air  are  mechanically  operated,  but 
the  action  of  the  governor  is  either  to  cut  off  the  supply  of  gas 
alone,  without  cutting  off  also  the  corresponding  supply  of  air; 
that  is,  the  governing  impoverishes  the  mixture;  or  to  throttle 
the  mixture  of  gas  and  air.  By  the  vertical  arrangement 


176 


THE   GAS-ENGINE. 


the    crank-shaft    can    be    operated    in    an    oil-bath,    securing 
perfect  lubrication  of  the  crank-pins,  and  a  certain  amount  of 


.  33. 


spattering  of  the  oil  into  the  trunk  end  of  the  cylinder  secures  a 
lubrication  at  this  point.     The  valves  are  operated  by  cams  on 


* 
¥ 


GAS-ENGINES  BURNING    GAS.  177 

an  independent  shaft  a  outside  of  the  crank-case,  driven  by  spur- 
gears  at  half  the  speed  of  the  main-shaft.  The  cam  lifts  a  roll 
upon  a  pivoted  lever  b  whereby  the  large  poppet  admission- valve  c 
is  opened  at  each  charging  stroke.  The  admission  valve-stem 
carries  an  arm  d  by  which  its  rise  will  lift  the  gas-valve  stem  g 
and  admit  gas  to  the  mixing- chamber  through  the  gas- inlet  pipe  e. 
Air  enters  around  the  gas-valve  whose  stem  is  g  in  an  annular 
passage,  and  when  c  is  open  the  mixture  passes  to  the  cylinder  on 
the  charging  stroke.  The  action  of  the  governor  is  to  throw  out 
a  short  link  attached  to  g  so  that  the  rise  of  the  arm  d  will  fail  to 
hit  the  end  of  this  link.  The  gas-valve  does  not  open  in  this  case, 
but  air  only  enters  through  the  admission- valve;  hence  the  mixture 
is  not  ignited  in  the  following  stroke.  The  exhaust-valve  is. 
behind  the  admission- valve,  and  is  also  a  cam-operated  poppet. 
The  ignition  is  by  an  exterior  flame  or  hot  tubes  in  the  older  and 
smaller  forms  and  by  electricity  in  the  recent  and  larger  ones. 

71.  The  Korting  Engine. — In  the  Korting  engine  (Fig.  34) 
an  effort  is  made  to  secure  a  proper  proportioning  of  the  air  and 
gas  mixture  by  means  of  mechanical  aspiration  of  each  constituent 
in  a  separate  cylinder  (a  and  b)  whose  volume  is  proportioned 
to  the  desired  proportions  of  gas  and  air.     This  pair  of  cylinders 
may  be  single-  or  double-acting  and  is  on  a  common  rod,  and  the 
pistons  are  to  act  as  the  displacing  pistons  in  the  Clark  engine, 
with  a  positive  proportioning  instead  of  the  automatic  propor- 
tioning of  the  Clerk  design.     The  motor  cylinder  in  the  single- 
acting  type  receives  an  impulse  at  each  revolution,  since  it  is 
only  a  compressing  and  working  cylinder  and  is  not  compelled 
to  draw  in  the  charge.     The  governing  is  effected  by  diminishing 
the  proportion  of  time  during  which  the  displacing  pistons  are 
open  to  the  working  cylinder  or  to  the  admission  of  mixture. 
When  open  during  a  full  stroke  the  working  cylinder  receives  the 
maximum  charge.     When  open  less  than  this  the  charge  is  pro- 
portionally diminished,  while  its  relative  proportions  remain  un- 
affected. 

72.  The  Westinghouse  Engine. — Tn    the  vertical   gas-engine 
designed  by  the  Westinghouse  Machine  Co.,  and  shown  in  section, 


178  THE   GAS-ENGINE. 

in  Fig.  25,  there  are  three  vertical  cylinders,  each  operating  i.pon 
the  Otto  cycle.  By  the  use  of  three  cylinders  there  will  be  three 
impulse  or  working  strokes  in  two  revolutions  of  the  crank-shaft. 
Hence  there  is  only  one  less  working  or  impulse  stroke  than  would 
occur  in  the  single-cylinder  double-acting  steam-engine.  The 
valves  of  the  poppet  type  are  mechanically  operated  by  cams  on 
driven  shafts  which  are  geared  to  the  crank-shaft.  Air  and  gas 
are  admitted  in  desired  proportions  to  the  mixing-chamber  AT, 
and  when  the  admission- valve  J  is  opened  by  the  cam  B  and  lever 
C  the  charge  flows  into  the  cylinder  on  the  down  stroke.  On  the 
upward  stroke  the  charge  is  compressed,  and  at  the  upper  dead- 
centre  a  second  cam  on  the  shaft  B  closes  and  breaks  an  electric 
circuit  at  the  bottom  of  the  spark  or  igniting-plug  F.  The  pas- 
sage of  this  spark  ignites  the  charge  and  this  produces  the  working 
stroke.  The  exhaust-valve  E  is  lifted  by  the  cam  on  the  shaft  A 
by  the  roller  on  the  lever  G,  and  the  products  of  combustion  are 
exhausted  through  O.  Through  H  and  K  circulates  the  cooling 
water.  The  construction  illustrates  the  use  of  removable  plugs  or 
bonnets  for  convenient  access  to  the  valves.  The  governing  in  this 
engine  is  effected  by  a  fly-ball  governor  at  the  side  of  the  engine, 
shown  at  B  in  Fig.  36,  which  controls  the  areas  of  the  ports  through 
which  gas  and  air  are  admitted  to  the  mixing- chamber.  The  lever 
H  above  the  chamber  turns  a  cylindrical  valve  or  shell  by  which 
the  area  of  the  gas- port  is  adjusted  by  varying  the  length  of  the 
port  uncovered  to  the  passage  G.  The  lower  lever  H  similarly 
controls  the  air-port  D,  so  that  any  desired  ratio  of  gas  to  air  can 
be  fixed  upon  and  will  be  permanent  until  readjusted  by  hand. 
Pointers  over  graduated  arcs  indicate  the  relative  positions. 
Inside  these  cylindrical  shells  the  governing  valve  A  is  adjusted 
for  position  by  the  balls  of  the  governor  so  that  the  width  of  the 
two  ports  uncovered  is  made  to  vary  with  the  speed  of  the  engine  .f 
so  that  a  throttling  action  occurs  without  affecting  the  proportions 
of  the  mixture.  This  uniform  mixture  of  varying  volume  is 
fired  at  every  working  stroke.  The  amount  of  energy  is  deter- 
mined by  the  volume  which  fills  the  clearance  and  therefore  by 
the  compression  of  the  charge,  and  not  by  its  constitution  or  the 


35. 


("lo  f^ce  page  178.) 


G4S-ENGINES   BURNING   GAS. 


179 


proportion  of  combustible  in  it.  When  the  gas  changes  in  quality 
or  richness,  an  adjustment  of  the  relative  areas  of  gas  and  air 
introduced  in  the  mixing-valve  makes  the  necessary  adjustment 
for  such  change.  A  convenient  provision  on  the  cam-shaft 
enables  one  of  the  three  cylinders  to  be  disconnected  from  the 


FIG.  36. 

inlet  service  of  gas  and  air,  so  that  this  cylinder  can  be  connected 
with  a  reservoir  of  compressed  air  to  operate  as  an  air-engine 
and  turn  the  engine  over  until  the  other  two  cylinders  have  begun 
their  normal  function  of  compression  and  ignition.  The  sliding 
of  the  starting-cam  on  the  shaft  can  then  throw  the  air-inlets  from 
the  air- reservoir  out  of  action  and  the  gas-inlets  come  into  service. 
For  the  larger  sizes  of  engine  developing  several  hundred 
horse-power  the  horizontal  arrangement  of  cylinder  is  preferred 
(Fig.  37),  and  in  this  design  the  desired  smooth  and  regular 


i8o 


THE   G4S-ENGINE. 


action  can  be  secured  by  using  the  two  cylinders  in  tandem,  making 
a  double-acting  engine. 

73.  The  Two-cycle  Engine. — The  term  "two  cycle"  has 
been  applied  to  those  forms  of  engine  in  which,  as  in  the  deriva- 
tives of  the  Clerk  design,  an  impulse  or  working  stroke  takes  place 


FIG.  37. 

once  in  each  revolution.  This  is  nearly  always  secured  by  the 
expedient  of  closing  the  front  or  crank  end  of  the  cylinder  or  the 
crank-case,  so  as  to  make  this  end  serve  to  draw  in  the  charge  and 
displace  it  into  the  back  end,  where  it  is  finally  compressed  and 
ignited.  This  construction  compels  the  exhaust-ports  to  be 
located  as  in  the  Clerk  engine,  in  the  side  of  the  cylinder-bore,  so> 
as  to  be  uncovered  by  the  piston  just  before  it  reaches  its  outer- 
most position.  The  pressure  of  the  gases  from  the  front  or  dis- 
placer  end  will  help  to  carry  the  exhaust  gases  out,  but  care  must 
be  taken  to  prevent  the  escape  of  fresh,  unused  mixture  through 
the  exhaust-port  by  having  this  latter  uncovered  too  long.  Any 
products  of  combustion  which  remain  behind  the  working  face 
of  the  piston  act  to  heat  the  incoming  mixture  and  to  increase  its 
volume  and  pressure  while  diminishing  its  weight  and  density, 


GAS-ENGINES  BURNING    GAS. 


181 


and  also  serving  to  dilute  the  composition  of  this  new  mixture 
There  has  been  an  opinion  that  the  mixture  and  the  products  of 
combustion  have  a  tendency  to  stratify  behind  the  piston,  but 
the  existence  of  this  action  is  decidedly  questionable. 


FIG.  38. 


FIG.  39. 


In  a  successful  form  of  two-cycle  engine  (Figs.  38,  39,  and  40) 
the  mixture  of  carbureted  air  enters  from  the  carburetor  (see 
Chapter  X)  through  the  opening  A  into  the  crank-case  on  the 
upward  stroke  of  the  piston.  The  downward  or  working  stroke 
(Fig.  38)  after  the  ignition  of  the  working  charge  above  the  piston 
slightly  compresses  this  mixture  in  the  case  so  that  it  tends  to 
escape  through  the  channel  at  the  left  of  the  cylinder  as  soon  as 
the  descent  of  the  piston  shall  uncover  the  upper  end  of  it. 
The  descent  of  the  piston  first  uncovers  the  exhaust-port  F  at  the 


182 


THE  GAS-ENGINE. 


right  (Fig.  39),  and  the  burnt  gases  flow  out  as  shown  by  dotted 

arrows.  The  enlarging  volume 
of  the  exhaust-pipe  lowers  the 
velocity  of  the  escaping  gases 
and  lessens  the  noise.  The  fur- 
ther descent  of  the  piston,  now 
nearing  its  lower  dead-centre, 
uncovers  the  inlet-port  C  (Fig. 
40)  when  the  compression  in  the 
crank-case  is  the  greatest,  where- 
upon the  fresh  mixture  flows 
into  the  volume  above  the  pis- 


FIG.  40. 


FIG.  253 


ton,  now  at  its  greatest  value,  filling  this  with  the  new  charge. 
The  deflector  G  (shown  in  more  modern  form  in  Fig.  253  and 
in  better  detail)  throws  the  charge  of  fresh  mixture  awiy  from 
the  open  exh  .ust-port  and  up  eg  Jnst  the  top  he  d,  so  that  it  acts 
to  force  out  from  above  downward  any  burnt  g  ses  still  left 
behind  in  the  cylinder,  and  this  action  continues  until  the  ascent 
of  the  piston  closes  first  the  inlet-port  C  (Fig.  39)  and  then  the 
exhaust.  Compression  now  ensues  above  the  piston  after  both 
ports  are  closed  by  the  piston  (Fig.  38)  until  the  upper  de  d- 
centre  is  re  ched,  when  the  compressed  ch  rge  is  fired,  and  the 
working  stroke  is  m  de  ag  .in,  repeating  the  cycle. 


GAS  ENGINES  BURNING  GAS.  -83 

Fig.  252  shows  a  form  of  well  designed  engine  in  which  the 
piston  is  made  to  act  as  a  valve  on  the  inlet  passage  from  the 
carburetor.  The  piston  of  this  engine  (Fig.  253)  shows  modern 
aspects  of  the  deflector. 

The  simplicity  ,of  this  cycle  has  attracted  many  designers 
and  users,  since  it  avoids  a  cam-shaft  and  has  only  a  valve  on 
the  inlet  connection  which  enters  at  A  from  the  carburetor, 
if  even  this.  Hence  many  parts  are  dispensed  with,  in  some 
cases  running  over  100  in  a  multi-cylinder  engine.  Its 


Spark  Hug 


Fin.  252. 

principal  objections  are  the  difficulty  of  regulating  it  closely  to 
speed,  and  the  trouble  which  arises  when  under  variable  resistance 
it  happens  that  the  combustion  of  the  charge  has  not  been  com- 
plete when  the  inlet  opens  (Fig.  40).  When  the  space  D  above 
the  piston  has  flame  in  it,  and  the  port  C  is  opened,  the  flame  will 
run  back  and  ignite  the  mixture  stored  in  the  crank-case,  and  it 


184 


THE   GAS-ENGINE. 


may  not  be  renewed  again  sufficiently  soon  to  keep  the  engine 
turning  against  its  load.  Premature  ignitions  result  sometimes 
from  the  fact  that  the  compression  is  necessarily  invariable,  and 
particularly  if  there  are  any  projections  which  gradually  become 
red-hot.  The  deflector  G  is  kept  cool  enough  not  to  give  trouble 
from  this  cause  by  the  blowing  action  upon  it  of  the  relatively 
cool  current  of  fresh,  charge.  Fig.  252  shows  the  arrangement 
which  results  when  both  inlet  and  exhaust-ports  come  in  the 
plane  of  the  rotation  of  the  cranks  as  in  multi-cylinder  engines. 

74.  Comparison  of  Types. — For  a  full  mathematical  and 
analytical  treatment  of  cycles  independent  of  the  mechanisms 
which  utilize  them  the  reader  is  referred  to  Chapter  XVII.  But 
for  the  present  purpose  a  summary  consideration  of  the  cycles 
in  connection  with  the  engines  which  utilize  them  would  bring 
out  the  following  results: 

C  a  certain  mass  of  gas, 
Given  x    the  same  compression, 

^  the  same  heat-supply  after  compression, 

there  will  be  the  same  work  done  and  hence  the  same  efficiency 
in  the  cycles  of 

Carnot, 
Otto, 
Bray  ton. 

For  the  reasons  for  this  conclusion  reference  should  be  had 
to  the  full  treatment  later  in  this  volume  (Chapter  XVII). 

If,  further,  a  comparison  be  made  to  ascertain  the  highest, 
lowest,  and  intermediate  values,  the  following  table  results: 


Item. 

Lowest. 

Intermediate. 

Highest. 

Maximum  temperature  

Carnot 

Bray  ton 

Otto 

Pressure  lange   .  . 

Bravton 

C  a.  root 

Otto 

Volume  Tang" 

Otto 

Bray  ton 

Carnot 

TempcTaturc  range.  .  . 

Carnot 

Bravton 

Otto 

Mean  effective  pressure  

Carnot 

Bravton 

Otto 

Mean  effective  temperature  

Carnot 

B  rayton 

Otto 

Pressure  range 

Bravton 

Carnot 

Otto 

Mean  effective  pressure 

GAS-ENGINES  BURNING   GAS.  185 

The  Diesel,  being  regarded  as  a  modified  Carnot,  can  be 
brought  into  this  grouping. 

It  does  not  necessarily  follow  that  the  maxima  of  theory  are 
the  most  convenient  or  practicable  in  practice.  For  example, 
while  the  Carnot  holds  the  first  place  so  far  as  maximum  tem- 
perature is  concerned,  its  impracticability  gives  the  place  to 
Bray  ton.  Since  neither  pressure  range  nor  large  work  area  per 
stroke  is  wanted  by  itself,  but  only  the  ratio  between  them,  Brayton 
holds  the  most  favorable  place,  since  it  is  to  this  ratio  that  the 
weight  of  the  engine  will  be  approximately  proportional.  The 
volume  range  should  be  low,  which  is  the  great  advantage  of  the 
Otto.  The  mean  effective  temperature  should  be  low,  and 
Carnot  is  the  only  one  which  exceeds  the  Brayton  in  this  matter. 
The  low  mean  effective  pressure  of  the  Carnot  and  all  other 
isothermal  combustion  cycles  puts  them  out  of  consideration  in 
comparison  with  Otto  and  Brayton. 

It  is  not,  however,  a  matter  of  indifference  as  to  the  means  used 
to  get  the  heat  into  the  working  medium.  When  the  air  contains 
varying  degrees  of  moisture,  so  that  the  fuel  becomes  not  only 
carbonic  acid  upon  burning  in  the  air,  but  there  is  also  a  propor- 
tion of  steam  present,  what  value  should  be  used  for  the  specific 
heat  in  such  a  combustion?  (par.  55).  In  the  second  place,  the 
chemical  change  is  accompanied  by  a  change  in  the  intrinsic 
volume  (par.  14).  It  is,  furthermore,  likely,  in  the  third  place, 
that  a  fuel  may  give  out  more  heat  when  burned  in  one  way  than 
when  burned  in  another. 

75.  Other  Forms  of  Gas-engine. — In  the  foregoing  enumer- 
ation of  types  of  gas-engine  motor  a  certain  limited  number  only 
have  been  referred  to.  A  modification  from  these  designs  has 
been  much  favored  in  England  and  is  coming  into  use  in  auto- 
mobile practice  in  this  country,  in  which  the  two  cylinders  oper- 
ating on  a  common  crank- shaft  are  put  on  opposite  sides  of 
the  crank- shaft  with  the  crank  revolving  between  them.  Both 
cylinders  may  take  hold  upon  a  common  crank-pin,  or  they  may 
be  connected  to  separate  cranks.  When  they  take  hold  upon  a 


i86  THE  GAS-ENGINE. 

common  pin  and  lie  in  the  same  axial  line,  the  two  cylinders  can 
be  tied  together  conveniently  so  as  to  take  off  some  of  the  shock 
or  jar  due  to  the  liberation  of  forces  inside  the  cylinder.  This 
arrangement  is  known  as  the  opposed  or,  sometimes,  the  double- 
opposed  system.  The  use  of  four  cylinders  is  coming  increasingly 
into  use  for  automobile  practice  by  reason  of  the  action  of  this 
system  in  causing  four  impulses  in  every  two  revolutions  of  the 
shaft.  This  gives  the  same  quality  of  turning  effort  as  is  given 
by  the  steam-engine,  provided  the  ignitions  are  suitably  timed. 
This  four-cylinder  system  has  also  the  advantage  that  in  nearly 
all  circumstances  one  of  the  four  cylinders  will  have  in  it  a  com- 
pressed mixture  ready  to  be  ignited,  so  that  if  a  spark  can  be  fired 
in  all.  cylinders  at  once,  with  the  transmission-gear  detached  from 
the  motor-shaft,  the  engine  becomes  self-starting  if  the  pistons 
are  tight  enough  to  have  held  the  mixture  from  escape  by  leakage, 
and  the  motor  was  stopped  with  the  igniting  device  either  out  of 
action  or  set  considerably  behind  (pars.  140,  164). 

There  has  been  proposed  by  certain  of  the  English  designers 
a  plan  to  have  the  exhaust-gases  which  remained  in  the  combus- 
tion space  swept  out  or  to  have  the  cylinder  and  combustion- 
chamber  "  scavenged  "  by  pure  air  so  that  the  combustible  charge 
should  be  a  mixture  of  gas  and  air  without  exhaust-gases  as 
diluents.  In  this  system  advantage  is  taken  of  the  oscillations 
or  waves  of  pressure  which  occur  in  the  exhaust- pipe,  due  to 
the  inertia  of  the  discharge  from  the  cylinder.  The  high- pressure 
discharge  being  succeeded  by  a  less  pressure,  it  is  possible  to 
make  the  period  of  this  diminished  pressure  coincide  with  the 
approach  of  the  piston  to  the  end  of  its  exhaust-stroke.  If  the 
exhaust-valve  is  kept  open,  in  communication  with  this  space  of 
diminished  pressure  and  the  charge  or  air- inlet  valve  is  held  open, 
while  the  exhaust-valve  is  also  open,  a  charge  of  pure  air  comes  in 
through  the  combustion  space  and  sweeps  the  burned  gases  from 
before  it.  There  have  also  been  designs  proposed  with  unusual 
arrangements  of  the  mechanisms  so  that  the  volumes  swept  through 
by  the  piston  should  be  different  for  the  different  phases  of  the 


GAS -ENGINES   BURNING    GAS,  187 

cycle  so  as  to  secure  a  maximum  increase  of  volume  in  the  expan- 
sion stroke  and  lower  the  terminal  pressure  when  exhaust  opens. 
These  designs  are  due  to  Mr.  Atkinson  of  England.  The  advan- 
tages offered  by  the  theory  of  these  designs  have  been  more  than 
offset  by  the  inconvenience  and  complication  of  the  mechanism 
with  which  they  were  carried  out.  Combinations  are  also  in  use 
with  the  Clerk  arrangement  of  exhaust-port  opened  by  the 
piston,  with  the  ordinary  cam-driven  exhaust-valve.  The  arrange- 
ment'of  cylinders  tandem  on  a  single  piston-rod  (Fig.  37)  forms 
another  modification. 

76.  The  Compound  Gas-engine. — The  compound  gas-engine 
is  also  a  further  modification  in  which  the  expansion  of  the  gas, 
after  ignition,  keeps  on  by  continuous  action  through  two  cylinders 
of  successively  increasing  volume,  instead  of  being  completed  in 
one  cylinder  only.  The  purpose  of  compounding  is  to  diminish 
the  terminal  pressure  at  which  the  expanded  mixture  leaves  the 
engine  and  thus  utilize  the  heat  energy  of  the  charge  more  com- 
pletely. It  also  acts  to  diminish  exhaust  noise.  The  difficulties 
in  the  way  are  those  which  attach  to  the  loss  of  pressure  and  heat 
incident  to  a  free  expansion  between  the  two  cylinders,  which 
causes  a  heat  loss  greater  than  is  regained  by  the  longer  range  of 
the  expansion.  The  second  cylinder  increases  the  engine  friction,, 
and  the  additional  work  which  it  gives  out  is  small  compared  to 
the  work  done  in  the  first  one.  If  the  attempt  is  made  to  get 
more  out  of  the  second  cylinder  in  the  way  of  crank-pin  effort, 
it  becomes  of  larger  volume,  with  the  friction  proportionately 
increased.  The  second  cylinder  will  always  be  colder  than  the 
first,  and  the  passage  of  the  hot  gases  into  it  causes  a  loss  or  drop 
of  pressure  or  volume  by  this  chilling  action  which  is  not  regained 
in  work.  The  general  opinion  concerning  the  compound  engine 
to  date  has  been  that  the  gain  was  not  worth  the  sacrifices  made 
to  secure  it. 


CHAPTER  VI. 

GAS-ENGINES  USING  KEROSENE  OIL. 

77.  Introductory. — The  only  difference  between  an  internal- 
combustion  engine  using  kerosene  oil  and  ihe  gas-engine  proper  is 
that  the  oil-engine  requires  a  device  whereby  the  liquid  fuel  may 
"be  atomized  or  pulverized  so  as  to  be  introduced  into  the  mixture 
In  a  state  of  such  fine  division  that  the  liquid  fuel  in  a  condition 
analogous  to  a  mist  shall  be  distributed  all  through  the  mixture 
of  oil  and  air  in  such  a  condition  that  the  propagation  of  flame 
shall  be  instantaneous  or  practically  so.  as  it  is  in  a  mixture  of 
air  and  gas.     The  difficulty  of  governing  in   the  oil-engine  is 
somewhat  greater  than  in  the  gas-engine,  since  a  drop  of  liquid 
oil  makes  a  considerable  volume  of  gas  when  vaporized      If  a 
slight  excess  of  liquid  fuel  is  injected  into  the  mixture  above  that 
which  the  mixture  can  handle  with  complete  combustion,   the 
liquid  fuel  is  broken  up  by  the  heat  and  is  either  oxidized  or  dis- 
sociated.    If  simply  oxidized,  it  burns  as  a  liquid  in  the  cylinder 
and  exhaust- passages,  making  an  unpleasant  odor  and  depositing 
soot.     If  dissociated,  the  volatile  elements  burn  off  and  leave 
behind  a  carbon  residue  which  coats  the  surfaces  and  clogs  the 
passages.     It  is  the  variation  in  composition  of  crude  petroleums 
which  makes  it  practically  impossible  to  use  them  directly  in  oil- 
engines.    The  volatile  parts  will  vaporize  and    the  less  volatile 
will  be  deposited,  forming  coatings  and  clogging  cylinders  valves, 
and  passages 

78,  The  Priestnxan  Engine.— The  Pnestman  enp'ne  was  one 
of  the  earliest  to  use  kerosene  in  liquid  form      It  was  a  four- phase 

1 88 


GAS-ENGINES   USING  KEROSENE  OIL.  189 

or  Otto  cycle  engine  with  electric  ignition.  A  jet  of  kerosene 
is  forced  by  air-pressure  maintained  by  a  pump  in  a  reservoir 
into  a  jet  or  current  of  air  from  that  same  reservoir.  The  kero- 
sene meets  the  air,  which  attacks  it  in  annular  form  and  atomizes 
or  pulverizes  it.  The  atomized  oil  in  a  vehicle  of  air  enters  a 
vessel  called  a  vaporizer,  which  is  kept  hot  by  the  exhaust-gases 
which  are  in  a  jacket  surrounding  the  vaporizing-chamber  On 
the  out-stroke  of  the  piston  the  mixture  from  the  vaporizer  passes 
into  the  cylinder  behind  the  piston  with  the  necessary  supply  of 
additional  air  to  make  an  explosive  mixture.  The  mixture  is 
compressed  by  the  return  of  the  piston,  and  is  fired  by  the  spark 
from  an  induction-coil. 

To  start  the  engine  a  hand-pump  had  to  be  operated  to  get 
pressure  to  force  the  oil  through  the  spraying-nozzle,  and  by 
means  of  an  external  lamp  the  vaporizer  was  heated.  When  the 
vaporizer  was  hot,  the  engine  was  started  in  the  usual  way. 

In  this  engine  governing  was  effected  by  throttling  the  oil  and 
air-supply  and  the  effort  made  to  maintain  the  proportions  by 
weight  of  oil  and  volume  of  air.  The  compression  pressure  of 
the  mixture  before  ignition  is,  however,  steadily  reduced  as  the 
load  is  reduced,  so  that  at  very  light  loads  the  engine  would  run 
almost  as  a  non-compression  engine.  The  vaporizer  was  liable 
to  become  flooded  with  oil,  which  lowered  its  temperature  on 
the  one  hand,  and  if  anything  happened  to  make  the  vaporizer 
too  hot,  the  oil  would  decompose  with  a  deposit  of  carbon  as  the 
result. 

79.  The  Hornsby-Akroyd  Engine. — The  more  successful 
British  form  of  the  kerosene  engine  is  known  as  the  Hornsby- 
Akroyd.  The  kerosene  is  carried  in  a  chamber  from  which  it 
is  drawn  by  an  oil-pump  driven  from  the  valve-shaft.  This 
pump  sends  the  oil  to  a  water- jacketed  chamber  at  the  side  of  the 
cylinder  having  two  outlets.  One  of  these  is  a  by-pass  which  is 
operated  by  the  governor  permitting  the  return  of  excess  of  oil. 
When  the  by-pass  is  open  by  the  speed  of  the  governor,  the 
entire  capacity  of  the  oil- pump  is  returned  into  the  oil- reservoir. 


190  THE   GAS-ENGINE. 

When  it  is  closed  by  the  slowing  of  the  engine  and  the  increase 
of  the  load,  the  entire  capacity  of  the  pump  is  delivered  through 
the  other  opening,  which  is  a  small  needle-hole,  into  the  hot  chamber 
behind  the  piston  at  the  end  of  the  cylinder,  which  is  the  clearance 
or  combustion  volume.  This  chamber  is  first  heated  in  order 
to  start  the  engine  by  a  lamp  until  it  is  at  a  good  red  heat.  After 
the  engine  is  started  the  heat  of  compression  and  of  the  ignition 
of  the  oil  keeps  the  chamber  hot  enough  so  that  no  ignition  appa- 
ratus is.  needed.  The  oil,  being  injected  into  the  atmosphere 
of  air  in  the  chamber  and  heated  by  the  compression  and  the  hot 
walls,  becomes  a  gas,  and  the  compression  and  the  heat  of  the 
walls  fire  it  as  the  compression  reaches  its  maximum  at  the  end 
of  the  stroke.  If  the  load  on  the  engine  falls  off,  so  that  too  little 
oil  is  delivered  to  the  combustion-chamber,  it  cools,  and  little  by 
little  the  engine  will  slow  down  until  it  will  finally  stop.  The 
engine  is  therefore  at  its  best  under  a  constant  and  adequate 
load  which  will  keep  the  pump  in  normal  discharge  and  the 
vaporizing-chamber  at  normal  heat.  The  troubles  in  this  engine 
are  due  to  a  deposit  of  carbon  in  the  chamber  due  to  dissociation 
of  the  oil  at  high  temperatures  and  the  clogging  of  the  needle- 
hole  in  the  jet  either  from  carbon  or  from  some  impurity  in  the 
oil. 

80.  The  Secor  Kerosene-engine. — The  Secor  engine  (Fig.  41) 
is  an  American  design  in  which  the  external  vaporizer  is  dis- 
carded, and  in  which  the  liquid  oil  is  drawn  in  at  atmospheric 
pressure  with  the  necessary  air  by  the  aspirating  or  charging 
stroke  of  the  piston.  The  proportion  of  liquid  to  air  is  propor- 
tioned by  a  micrometric  adjustment  of  the  inlet-valve  controlled 
by  the  governor.  The  lack  of  precision  incident  to  a  forced  oil- 
supply  and  an  inhaled  air-current  is  thus  avoided.  The  fuel  and 
air  come  together  in  a  mixing-chamber,  which  is  only  warmed 
by  conduction  from  the  motor  cylinder.  Cam -operated  poppet- 
valves  are  used.  The  charge  is  ignited  electrically,  using  the 
hammer-break  system  described  later  in  Chapter  XI.  If  too 
much  oil  should  collect  in  the  mixing-chamber,  it  will  make  the 


FIG.  41. 


(To  face  pae.e  190.) 


GAS-ENGINES   USING  KEROSENE  OIL. 


191 


governing  sluggish  under  varying  loads,  since  several  revolutions 
must  take  place  before  the  governor  can  effect  the  passage  of  oil 
into  the  mixing-chamber. 

81.  The  Mietz  and  Weiss  Engine. — The  Mietz  and  Weiss 
kerosene- engine  represents  the  two-phase  type.  It  requires, 
therefore,  that  the  crank-chamber  should  be  enclosed  in  order  that 
a  moderate  compression  of  air  may  be  effected  on  the  outgoing 


FIG.  42. 

or  working  stroke  of  the  piston.  An  eccentric  on  the  shaft  of 
the  engine  operates  a  small  plunger  by  which  the  oil  is  injected 
into  the  cylinder.  This  oil  is  delivered  upon  a  conical  vaporizer 
which  is  preheated  by  a  lamp  in  starting  the  engine,  but  which 
is  kept  hot  by  the  ignitions  after  the  engine  is  moving.  The  air 
charge  is  received  from  the  crank-chamber  through  a  port  which 
is  opened  at  the  end  of  the  impulse  stroke  after  the  larger  exhaust- 
port  has  been  first  opened  through  which  the  previous  charge 


THE  GAS-ENGINE. 


escapes.  A  projection  or  deflector  on  the  piston  directs  the  in- 
coming charge  towards  the  head  of  the  cylinder  and  away  from 
the  exhaust-ports  as  in  Figs.  38-40.  A  small  valve  at  the  end 


FIG.  43- 

of  the  oil-pump  cylinder  limits  the  amount  of  oil  injected,  and  the 
governing  is  done  by  a  push-blade  which  is  lifted  to  miss  contact 
with  the  plunger  if  no  charge  cf  oil  is  desired.  This  engine  is 
also  made  into  a  two-phase  gas-engine  by  a  very  simple  conver- 
sion involving  only  the  omission  of  the  oil  system. 


GAS-ENGINES   USING  KEROSENE  OIL.  193 

82.  The  Diesel  Engine.     The  Hirsch  Engine.— The    Diesel 

engine  is  an  effort  to  secure  the  realization  of  the  Carnot  cycle 
by  having  the  heating  of  the  gas  take  place  at  constant  tempera- 
ture. It  was  presented  in  1897  by  Mr.  Rudolph  Diesel.  The 


•<" 


FIG.  44. 

kerosene-oil  fuel  is  injected  by  a  pump  into  the  cylinder  at  the 
end  of  an  adiabatic  compression  of  the  air  drawn  into  the  cylinder 
on  the  aspirating  stroke.  Figs.  42  to  44  show  sections  of  the 
Diesel  engine  as  variously  designed,  and  Fig.  45  is  its  characteristic 
indicator-card.  To  secure  a  high  value  for  the  initial  tempera- 
ture, and  a  high  range  of  pressure  the  compression  of  the 


194  THE   GAS-ENGINE. 

.air  is  made  to  approximate  500  pounds  per  square  inch.  The 
oil  entering  into  this  heated  atmosphere  is  at  once  raised  above 
the  temperature  of  ignition,  so  that  it  burns  with  a  utilization 
of  the  necessary  weight  of  air.  In  order,  however,  to  secure 
a  further  addition  of  heat  to  make  the  addition  approximate  an 
isothermal  addition,  a  further  quantity  of  oil  may  be  admitted 
so  as  to  maintain  a  constant  temperature  as  the  gas  is  expanded 
up  to  the  point  at  which  the  governor  should  cut  off  a  supply  of 
fuel.  After  the  cut-off  of  the  fuel-supply  an  attempt  at  adiabatic 
expansion  sets  in  and  is  continued  to  the  end  of  the  stroke.  The 
cylinder  is,  therefore,  necessarily  made  longer  and  of  smaller 
cross-section.  The  air  is  delivered  into  the  cylinder  against  the 
compressed  air  within  it  by  pressure  from  a  separate  pump.  The 


injection  of-  oil  is  once  in  each  two  complete  revolutions  as  in  the 
Otto  cycle. 

The  F.  C.  Hirsch  motor  illustrated  in  Fig.  46  operates  on 
essentially  the  same  principle  as  the  Diesel.  The  jet  of  oil  enters 
the  hot  bulb  at  the  top  of  the  cylinder  at  the  moment  when  this 
is  filled  with  hot  compressed  air  from  the  compression  or  upward 
stroke.  The  heat  of  the  walls  and  of  the  compression  gives  an 
initial  heat  and  pressure  to  the  air  sufficient  to  raise  the  oil  to 
ignition-point  and  still  further  raise  the  initial  pressure  of  the 
working  stroke.  In  the  card  in  Fig.  47  this  initial  pressure  is 
1 80  pounds  at  320  revolutions  per  minute,  giving  a  mean  pressure 
of  74.2.  The  oil-supply  is  regulated  by  a  governor,  or  can  be 


GAS-ENGINES   USING  KEROSENE  OIL.  195 

controlled  in  marine  use  by  a  thumb-screw  operating  a  needle- 
valve.  The  engine  is  started  by  warming  the  bulb  by  a  Primus 
lamp  for  six  to  ten  minutes;  after  one  or  two  turns  of  the  starting- 
crank  the  engine  should  take  care  of  itself,  and  the  heating-lamps 


Fir..  46. 

may  thereafter  be  put  out.  In  this  motor,  as  in  the  Diesel  there 
can  be  no  pre-ignition,  since  the  compression  is  on  pure  air  without 
fuel.  The  latter  is  introduced  only  close  to  the  dead-centre. 
There  can  be  no  condensation  of  liquid  fuel  in  the  cylinder,  with 
consequent  irregular  action  and  offensive  odor  to  the  exhaust. 

83.  The     Ver    Planck  -  Lucke     Kerosene-engine.  —  Messrs. 
Wm.  E.  Ver  Planck  and  Charles  E.  Lucke  have  designed  and 


196 


THE  GAS-ENGINE. 


operated  a  kerosene-engine  in  which  the  liquid  fuel  is  heated  so 
that  it  gives  off  a  vapor  from  the  liquid  until  the  tension  in  the 
closed  chamber  containing  the  kerosene  amounts  to  about  10 


pounds  per  square  inch.  The  heating  is  done  at  first  by  an 
exterior  lamp  like  a  plumber's  torch,  but  afterward  the  pressure 
is  maintained  by  the  heat  from  the  exhaust-gases,  The  kerosene 
vapor  from  this  closed  reservoir  is  delivered  to  a  mixing  and 
proportioning  valve  so  located  that  the  vapor  cannot  condense 
in  transit.  The  oil  vaporized  at  this  valve  meets  and  mixes  with 
a  similarly  controlled  air-current.  As  cold  air  is  used,  fairly 
high  compressions  are  possible,  much  higher  than  with  the 
hot-bulb  systems.  All  vapor  that  may  have  partly  condensed 
to  form  a  cloud  on  the  suction  is  re-evaporated  the  next  instant 
on  the  compression  when  the  mixture  has  the  lowest  possible 
temperature  for  the  compression  pressure.  Ignition  is  by  electric 
spark. 

Should  a  sudden  load  through  a  demand  for  a  large  amount 
of  vapor  result  in  a  lowered  pressure  in  the  boiling-chamber,  there 
would  result  instantly  a  great  evolution  of  vapor  to  meet  the 
supply  from  the  heat  in  the  kerosene  which  has  a  temperature 


G4S-ENGINES   USING    GASOLINE.  197 

due  to  the  higher  pressure,  and  is  therefore  superheated  for  any 
lower  pressure.  As  there  is  always  a  mass  of  liquid  oil  present 
in  the  kerosene  boiler,  its  temperature  can  never  rise  enough  to 
cause  decomposition  and  deposit  of  coke.  The  boiling  and  feed- 
ing is  continuou  ;  all  excess  vapor  passes  into  a  water- jacketed, 
liquid-kerosene  feed-pipe,  where  it  is  condensed  and  returned 
for  re- evaporation. 

84.  Comparison  of  Types.- — The  introduction  of  the  succes'sf  ul 
atomizing  and  vaporizing  carburetor  has  been  the  most  notable 
step  in  putting  the  various  types  of  kerosene-engine  upon  prac- 
tically the  same  footing.  It  has  become  obvious  that  for  the 
satisfactory  working  of  kerosene  it  must  be  pulverized  or  broken 
up  by  the  atomizing  method  and  vaporized  before  entering  the 
cylinder,  in  order  to  give  the  best  results,  particularly  where  the 
load  varies  (see  par.  32).  Where  the  carbureted  air  enters  the 
cylinder  in  gaseous  form  under  all  variations,  the  efficiency  of 
the  various  types  will  approach  each  other.  The  superior  effi- 
ciency ol  tne  Diesel  type  over  the  others  results  from  the  high 
compression  and  from  the  fact  that  the  combination  of  atomizing 
and  vaporizing  takes  place  at  such  a  high  temperature  as  to  make 
the  average  temperature  of  the  absorption  of  heat  higher  than 
in  the  other  types,  and  because  it  occurs  in  the  presence  of  an 
excess  of  air,  so  that  the  combustion  of  the  oil  is  practically  com- 
plete in  an  atmosphere  of  air  supporting  combustion.  Previous 
to  the  introduction  of  the  carburetor,  kerosene-engines  only 
worked  well  under  conditions  of  constant  load. 


CHAPTER  VII. 

• 

GAS-ENGINES  USING  GASOLINE. 
AUTOMOBILE     ENGINES. 

85.  Introductory. — When  it  became  necessary  to  furnish 
motors  of  light  weight  for  mechanically  dirven  bicycles  and 
horseless  vehicles,  attention  was  at  once  directed  to  the  use  of 
air  carbureted  by  liquid  gasoline  to  make  a  gas  to  use  in  the 
cylinder.  For  this  class  of  service,  where  light  weight  was  the 
prime  requisite,  the  high-speed  engine  was  at  once  decided  on. 
It  was  further  often  of  advantage  to  use  both  ends  of  the  cylinder, 
so  that  the  type  called  the  two-cycle  type  has  been  much  used. 
Gasoline  was  preferred  to  kerosene,  since  it  carburets  the  re- 
quired air  more  rapidly  and  certainly,  without  the  application 
of  an  exterior  source  of  heat.  It  could  be  obtained  readily  in 
ordinary  stores  in  small  villages  and  towns,  and  became  the 
accepted  source  of  heat  in  spite  of  the  elements  of  danger  resulting 
from  its  volatile  character.  It  is  usually  carried  in  tanks,  either 
under  atmospheric  pressure  or  under  a  very  slight  air-pressure 
sufficient  only  to  insure  its  displacement  to  the  motor  as  required. 
The  advantages  incident  to  its  use  have  brought  it  forward  for 
bicycles,  automobiles,  and  launches.  The  inconvenience  of 
carrying  water  for  the  cooling  of  the  cylinders  and  valves  of  such 
engines  has  introduced  what  is  called  the  air-cooled  motor,  in 
which  the  motion  of  the  cylinder  itself  through  the  air  should  be 
depended  on  to  cool  the  cylinder  to  the  necessary  point.  Where 
water  is  used  for  cooling,  it  will  usually  be  a  limited  weight  of 
it  which  will  be  cooled  by  circulating  through  a  radiator, — the 

19$ 


GAS -ENGINES   USING    GASOLINE.  IQ9 

« 

ladiator  bein^  air-cooled  for  lanci  practice  In  launch  practice 
the  water  in  which  the  boat  moves  can  be  used  for  cooling  directly 
or  for  cooling  the  radiator.  It  may  be  undesirable  to  circulate 
salt  water  containing  both  acids  and  mineral  salts  through  the 
water-jacket,  where  it  may  become  of  a  high  enough  temperature 
to  be  vaporized,  when  it  will  concentrate  the  acid  and  precipitate 
the  mineral  matter  with  n  the  jackets,  from  which  it  is  removed 
with  difficulty. 

86.  The  Air-cooled  Bicycle  Motor. — Fcr  operating  a  motor 
bicycle  or  light  tricycle  the  air-cooled  system  is  the  only  con- 
venient one.  In  order  to  keep  the  weight  of  the  motor  and  the 
load  on  the  tires  to  their  lowest  terms,  the  crank-  shaft  of  the  motor 
will  revolve  at  2500  revolutions  per  minute,  and  in  order  to  secure 
frequent  working  strokes  the  engine  will  be  of  the  two-cycle  type, 
giving  2500  explosions  per  minute.  If  the  arrangement  shown 
in  Fig.  50  be  selected,  for  example,  the  motor  cylinder  is  attached 
to  the  rear  member  of  the  frame,  so  as  to  bring  the  crank-shaft 
bearing  at  the  point  where  the  two  members  of  the  frame  join. 
The  reduction  of  speed  is  effected  by  a  belt  tiansmission  to  a 
flat  surface  forming  part  of  the  tire.  To  take  up  stretch  in  the 
belt  caused  by  dampness  and  use,  a  tightener  pulley  is  adjustable 
by  link  and  nut.  Chain  transmissions  are  of  course  not  open 
to  this  trouble,  but  are  less  silent.  The  gasoline  is  carried  in 
the  tank  hung  to  the  upper  member  of  the  frame  and  delivers 
by  gravity  to  the  carburetor  under  the  tank.  The  battery  and 
coil  for  the  ignition  are  under  the  saddle..  The  exhaust  passes 
into  a  muffler  under  the  lower  frame,  at  the  front.  It  will  be 
observed  that  the  cylinder  is  cast  with  deep  external  ribs,  so  as 
to  expose  a  large  radiating  and  contact  surface  to  the  air  as  the 
motor  moves  through  it,  and  cause  an  effective  air  cooling. 

To  compel  the  motor  to  make  the  first  few  strokes  necessary 
to  start  the  machine,  the  bicycle  is  fitted  with  the  ordinary  pedal 
equipment  with  coaster  brake,  so  that  by  starting  the  machine 
as  an  ordinary  bicycle  the  first  few  strokes  are  made  by  the  move- 
ment of  the  machine  itself.  The  presence  of  the  pedals  makes 


200 


THE   GAS-ENGINE. 


it  possible  to  operate  the  machine  by  foot-power  when  desirable. 
Uusally  there  is  an  arrangement  whereby  the  compression  on 
the  return  of  the  piston  in  starting  can  be  relieved  until  the  motor 
starts  its  cycle  regularly.  The  ignition  of  the  charge  is  by  electric 
spark,  which  can  be  advanced  or  retarded  or  prevented  by  a 
lever  on  the  handle-bar  or  between  the  knees  of  the  operator, 


FIG.  50. 


and  this  is  used  as  a  speed-control  as  well  as  the  throttle-valve, 
whereby  the  quantity  of  fuel  admitted  to  the  carburetor  may 
be  varied.  The  bicycle  conditions  favor  the  use  of  the  closed 
crank-case,  so  that  the  aspiration  stroke  draws  upon  the  mixture 
which  is  enclosed  around  the  crank  under  slight  tension.  A 
bicycle  with  a  motor  of  this  class  will  weigh  about  125  pounds,  and 
the  nominal  horse- power  of  the  motor  will  be  about  ij. 


GAS-ENGINES   USING    GASOLINE  201 

87.  The    Air-cooled  Automobile   Motor. — The   most   promi- 
nent and   successful  American  air-cooled   automobile   engine  is 
that  used  to  drive  the  Knox  automobile.     There  is  nothing  dis- 
tinctive, however,  except  the  construction  of  the  cylinder,  which, 
instead  of  a  water-jacket,  has  a  large  number  of  metallic  spines 
screwed  radially  into  the  walls.     A  fan  driven  by  a  belt  keeps 
up  a  good  circulation  of  air  through  and  around  these  spines, 
which  readily  conduct  the  heat  from  the  cylinder  walls  outward 
along  their  own  surfaces,  where  by  the  increased  surface  it  is  dis- 
sipated to  the  air  more  rapidly.     These  spines  are  made  of  \" 
round  iron  threaded  their  entire  length,  and  are  screwed  into  the 
walls.     If  the  surfaces  of  these  iron  rods  were  smooth  and  /  inches 
long  and  d  inches   in  diameter,  the  surface  for  radiation  from 
such  a  cylinder  would  be  increased  by  the  cylindrical  surface  of 
the  (n]  rods  or  by  ndln  square  inches.     If  also  by  threading  the 
entire  length  the  surface  were  increased  y  times,  so    that   the 
threaded  surface  =  yX plain  surface,   then  the  radiating  surface 
by  the  addition  of  n  threaded  spines  would  be  increased  xdlny 
square  inches 

Example. — 500  \"  spines  2"  long  in  which  the  threaded 
surface  is  1.4  t-mes  the  plain  surface  would  add 

22 

—  X  i  X  2  X  500  X  i  .4  =  i  TOO  square  inches. 

These  engines  cannot  be  built  in  large  sizes,  however,  the 
limit  being  about  .7  H.P.  in  one  cylinder,  by  reason  of  [he  im- 
possibility of  dissipating  large  quantities  of  heat  by  the  use  of 
a  medium  having  so  low  a  specific  heat  as  air. 

88.  The    Water-cooled    Automobile    Motor. — In    choosing    a 
representative  type  of  water-cooled  gasoline  automobile  engine 
it  would  seem  appropriate  to  select  for  such  type  the  Daimler 
engine.     It  was  in  1885  that  Mr,  Gottlieb  Daimler  patented  his 
high-speed  gasoline  engine,  and  in  the  same  year  Carl  Benz  of 
Mannheim,   Germany,  constructed  and  patented  his  first  gaso- 


202 


THE  GAS-ENGINE 


line  tricycles.  The  next  period  of  progress  brought  to  the  front 
the  French  designers  Peugeot,  Panhard,  De  Dion,  and  Mors.  The 
American  introduction  of  these  same  types  is  to  be  credited  to 
Haynes  &  Apperson  of  Indiana,  and  Winton  of  Cleveland. 

A  typical  Daimler  engine  would  be  such  a  one  as  is  shown 
in  Figs.  51  and  52,  having  four  cylinders  arranged  in  pairs  of  a 
cylinder  diameter  a  little  less  than  3^  and  of  stroke  a  little  less- 
than  4  inches.  The  crank- shaft  revolves  at  930  revolutions.  It 
operates  on  the  Otto  cycle,  with  the  inlet-valves  opening  auto- 
matically on  the  suction  stroke  and  the  exhaust- valves  mechani- 


Water  Outlet 


Induction  Valve 
Water  Inlet_ 

i. 

Exhaust  Valve 


Vapor  Pipe 
Throttle  Valve 

Connecting  Rod 
Carburettor 


Crankshaft 


FIG  51 

cally  driven  from  a  cam-shaft  turning  at  half  speed,  driven  from1 
the  motor-shaft  by  gears.  The  governing  is  effected  by  the  out- 
ward movement  of  weights  on  a  horizontal  shaft  whose  centrifugal 
tendency  is  counteracted  by  springs.  This  governor  throttles 
the  inlet  of  charge  into  the  cylinder  by  means  of  a  rod,  and  this 
same  rod  can  be  controlled  from  the  operator's  seat  for  varying 
speed  at  will.  The  cylinders  are  arranged  vertically,  which  is  the 


GAS-ENGINES   USING   GASOLINE. 


203 


most  convenient  arrangement  where  there  are  :  s  many  cylinders 
as  four  in  se  ies,  and  the  cylinders  are  water-cooled  by  the  circu- 
lation in  jackets  of  water  from  a  tank  by  means  of  a  centrifugal 
pump  driven  from  the  motor- shaft.  The  ignition  may  be  by  a  hot 
tube,  or,  in  order  to  secure  variations  in  the  point  of  ignition  and 
avoid  the  limits  set  by  the  hot  tube,  electric  ignition  can  also  be 
used.  For  convenience  of  access  for  inspection  and  repair,  the 


Water  Jacket 


Holes  for 
Sparking  Plugs 


Base  Chamber 


FIG.  52. 

valve-bonnets  are  held  down  by  covers,  seating  on  ground  joints, 
so  that  by  loosening  a  bolt  which  holds  down  a  dog  bearing  upon 
these  detachable  covers,  the  latter  can  be  removed  and  the  valves 
inspected.  The  details  of  transmitting  the  motion  of  the  motor- 
shaft  to  the  propelling  wheels  of  the  vehicle  are  aside  from  the 
present  purpose. 

89.  Variations  in  the  Automobile  Motor. — The  variations 
from  the. foregoing  typical  form  which  are  to  be  met  in  the  success- 
ful forms  of  the  present  day  cover  a  wide  range.  These  varia- 
tions are  often  of  commercial  origin  in  the  matter  of  affecting 
the  piice  at  which  the  motor  and  its  vehicle  can  be  sold,  as  well 
as  the  results  of  diffe  ence  in  selection  of  type.  The  engine  may 
have  three  vertical  cylinders  or  two.  The  motor  cylinders  may 
be  arranged  horizontally  instead  cf  vertically.  They  may  be 


204  THE  GAS-ENGINE. 

placed  on  opposite  sides  of  the  shaft,  if  arranged  horizontally, 
or  on  the  same  side.  They  may  be  of  the  two- phase  or  the  four- 
phase  system. 

They  may  d  ffer  in  their  methods  of  ignition,  although  the 
electric  system  in  one  or  the  other  of  its  forms  (par.  128),  by  reason 
of  the  c  nvenience  in  varying  the  time  of  ignition  has  practi- 
cally displaced  all  other  forms.  The  control  of  speed  by  the  hit- 
or-miss  method  of  governing  has  been  superseded  by  one  of  the 
other  forms  of  control,  and  the  throttle  system  controlling  both 
air  and  gasoline  is  the  one  which  is  in  most  frequent  use.  This 
control  of  the  motor  action  by  throttle  end  by  spark  gives  a  wide 
range  of  powder  and  of  speed  in  th:  motor  'tself  without  calling  for 
readjustment  in  the  transmission  machinery  between  the  motor 
and  the  propelling  wheels  of  the  vehicle.  This  double  control 
is  usually  attached  to  the  steering  column  of  the  car.  or  it  may  be 
operated  by  the  feet.  Probably  1200  revolutions  per  minute 
may  be  considered  as  the  normal  speed  of  motors  of  this  class. 
Their  horse-power  ranges  from  six  in  the  single- cylinder  designs 
to  thirty-five  and  forty,  and  even  sixty  or  eighty  horse- power  in 
machines  intended  exclusively  for  racing  upon  prepared  tracks. 
The  condition  in  motor  trucks  introduces  no  considerable  differ- 
ences in  the  motor  design,  but  mamiy  in  the  gearing  whereby  the 
speed  of  the  motor  is  reduced  to  that  of  the  propelling  wheels 
with  a  corresponding  gain  in  leverage  In  trucks  for  heavy  loads 
the  motor  requires  to  have  a  considerable  torque  in  order  to  start 
the  vehicle  from  rest  en  grades  or  on  a  rough  and  resistant  road- 
way. 

The  internal-combustion  engine  is  year  by  year  finding  a 
widespread  application  to  the  demands  of  heavy  motor  trucks. 

90.  The  Launch  Engine. — The  conditions  in  the  launch 
engine  resemble  those  in  the  motor  vehicle  except  that  the  load 
for  resistance  is  not  so  likely  to  vary  within  the  same  range  of 
limits.  The  variation  in  resistance  will  be  a  variation  in 
speed.  For  this  reason  the  two-cycle  design  has  been  a  favorite 
for  launch  practice,  and  in  the  Lozier  type  selected,  this  feature  is 


GAS-ENGINES  USING   GASOLINE.  205 

embodied  in  the  cycle  illustrated  in  paragraph  73,  Figs.  38,  39,  and 
40.  The  speed  and  power  are  varied  by  throttling  the  mixture. 
The  mixed  charge  slightly  compressed  in  the  crank- case  passes 
into  the  working  cylinder  at  the  end  of  the  working  stroke  and  is 
there  compressed  In  common  with  all  engines  of  this  design, 
if  the  mixture  is  impoverished  to  a  point  at  which  its  combustion 
is  retarded  and  is  not  completed  by  the  time  the  exhaust 
opens,  and  the  inlet- val  e  immediately  thereafter,  it  is  easily 
possible  for  a  flame  to  pass  through  the  inlet-valve  and  ignite  the 
mixture  in  the  crank-case  with  a  somewhat  disconcerting  report, 
and  of  course  a  stoppage  of  the  motor  until  the  crank-case  shall 
be  filled  again  with  a  fresh  unburned  mixture.  The  regularity  of 
the  resistance  in  launch  practice  is  favorable  also  to  the  employ- 
ment of  kerosene-engines.  An  increasing  development  of  recent 
years  has  been  the  introduction  of  auxiliary  gasoline-motors  into 
sailing  yachts  and  catboats.  Under  ordinary  circumstances  the 
sail  power  is  greatly  in  excess  of  the  power  of  the  auxiliary  en- 
gine, but  the  latter  can  be  used  when  the  wind  has  failed  or 
as  a  means  of  manoeuvring  the  boat  in  starting  and  in  landing 
without  reference  to  the  sail- power  The  requirement  of  such 
an  engine,  so  far  as  its  propelling  features  are  concerned,  is  that 
when  the  screw  is  not  turning  it  should  not  oppose  an  undue 
resistance  to  the  motion  of  the  boat.  Foi  this  reason  variable- 
pitch  screws  or  blades  whose  pitch  can  be  reversed  are  quite 
usual  By  reversing  the  pitch  the  engine  can  be  made  to  back 
the  boat  without  changing  the  direction  of  the  rotation  of  the 
mo  tor- shaft. 

g\  Converted  Gas-engines.  — It  will  be  apparent  that  any  of 
the  gas-engines  discussed  in  Chapter  V  can  be  made  into  gaso- 
line engines  when  they  are  to  be  used  in  places  where  gas  is  not 
natural  or  easily  manufaclured  by  a  very  simple  conversion.  All 
thai  needs  to  be  done  is  to  introduce  a  carbureting  device  of 
acceptable  form  (Chapter  X).  so  that  the  suction  stroke  shall 
draw  in  carbureted  air  instead  of  distinct  and  separate  supplies 
of  gas  and  air  through  t\vo  inlet-openings.  It  may  possibly 


206  THE   GAS-ENGINE. 

happen,  where  the  compression  volume  relatively  to  the  piston 
displacement  in  the'  design  of  the  engine  was  small,  that  the 
mixture  of  carbureted  air  rich  in  gasoline  will  give  trouble  from 
pre-igniting,  due  to  the  richness  of  the  mixture.  This  can  be 
corrected,  of  course,  by  impoverishing  the  mixture,  but  the  engine 
will  not  be  as  efficient  as  it  would  be  in  running  upon  a  fuel  for 
which  the  compression  volume  was  more  correctly  designed 
(pars.  152,  202). 


CHAPTER    VIII. 

ALCOHOL-ENGINES. 

92.  Introductory.  —  It  is  possible  to  carburet  the  charge  of 
air  entering  the  motor  cylinder  by  the  use  of  alcohol,  as  well  as 
by  either  kerosene  or  gasoline.  The  greatest  development  of 
the  alcohol- motor  has  been  in  Germany  and  France,  rather  than 
in  America,  for  reasons  of  a  purely  economic  rather  than  tech- 
nical sort.  The  high  revenue  tax  which  has  prevailed  hitherto 
upon  alcohol  as  a  feature  of  American  practice  has  made  it  less 
attractive  than  the  petroleum  derivatives  on  which  there  is  no 
such  tax.  In  France  and  Germany  there  has  been  a  govern- 
mental encouragement  towards  the  production  of  alcohol 
by  distillation  which  has  beei  lacking  in  America.  It  is 
not  usual  to  use  the  ethyl  alcohol  or  spirits  of  wine,  but  more 
usual  to  use  the  methyl  or  wood  alcohol  in  spite  of  its  pungent 
and  disagreeable  odor.  It  is,  again,  often  impossible  to  get 
alcohol  free  from  water,  and  in  automobile  practice  it  is  usual  to 
render  the  alcohol  non-potable  by  introducing  some  form  of 
hydrocarbon  to  a  degree  which  makes  it  unpalatable.  In  France, 
on  the  other  hand,  the  ethyl  alcohol,  from  the  prevalence  of  the 
vineyard,  is  more  used  than  the  wood-alcohol.  Recapitulating 
the  statements  in  paragraph  34,  it  should  be  noted  that  a  very 
usual  engine  mixture  in  use  quite  extensively  is  as  follows: 

Ethyl  90  per  cent 100      vols. 

Methyl  90  per  cent 10         " 

Hydrocarbon o. 50  " 

110.50  " 

What   is  designated  as  denatured  alcohol,  sometimes  called 
by    the    trade    name   of   electrine,  takes   the    above    mixture  of 

207 

' 


208  THE  G4S-ENG1NE. 

alcohols  and  adds  an  equal  volume  of  benzol.  This  mixture  has 
a  specific  gravity  of  0.835,  as  compared  with  water,  and  has  a 
calorific  power  of  13,150  B.T.U.  The  hydrocarbon  referred  to  in 
the  alcohol  mixture  is  usually  not  defined  beyond  that  it  should 
have  a  boiling-point  between  350°  and  440°  Fahrenheit. 

The  reader  is  referred  to  parag.  34  for  the  general  con- 
clusions of  recent  researches  on  the  use  of  alcohol  for  power. 
The  important  differences  are  in  the  use  of  a  greater  compression 
and  in  the  carburetor.  A  carburetor  to  handle  alcohol  requires 
to  be  hot  and  to  be  kept  at  a  higher  temperature  than  works 
satisfactorily  with  the  more  volatile  gasoline.  A  very  usual 
method  is  to  start  the  motor  with  gasoline,  using  a  gasoline  car- 
buretor, which  will  usually  perform  its  functions  while  the  engine 
is  cold.  After  the  engine  has  become  well  heated  the  gasoline 
is  shut  off  and  the  other  part  of  the  carburetor  is  turned  upon 
alcohol.  Fig.  69  illustrates  the  Marienfelde  form  of  duplex 
carburetor  for  gasoline  and  alcohol. 

93.  Alcohol-automobile  Motor.  The  Gobron-Brillie".  Since 
the  use  of  alcohol  as  fuel  has  not  been  extensive  as  yet  in 
America,  the  student  has  to  turn  to  French  sources  for  an  example 
of  an  alcohol-motor.  The  type  selected  might  be  any  of  the 
gasoline  types,  fitted  with  such  form  of  carburetor  (Chapter  X) 
as  should  be  adapted  to  work  with  alcohol.  The  engine  part 
would  require  no  modification.  For  a  type  specially  designed 
for  the  use  of  alcohol  probably  one  of  the  most  interesting  is  the 
Gobron-Brillie,  illustrated  in  Fig.  48. 

This  engine  is  fitted  with  two  pistons  in  one  cylinder,  one 
through  a  direct  and  the  other  through  a  back-acting  connecting- 
rod  acting  on  the  same  crank- shaft.  The  two  cranks  are  set  at 
1 80°.  The  arrangement  selected  is  for  a  two-cylinder  engine 
carrying,  therefore,  four  pistons;  the  two  lower  pistons  act  on  a 
single  crank.  The  carburetor  (Chapter  X)  is  designed  especially 
to  keep  the  mixture  constant  in  proportion  by  mechanical  means. 
A  spindle  is  rotated  by  the  machine  through  a  small  angle  by  a 
ratchet.  Corresponding  to  each  ratchet  tooth  is  a  small  bucket 
on  a  wheel  inside  the  carburetor  casing.  These  buckets  pick 


AL  COHOL-ENGINES. 


209 


up  the  alcohol  from  the  bottom  of  the  feed-chamber  and  deposit 
the  measured  amount  in  the  aspiration-pipe  where  it  meets  the 
inrushing  stream  of  heated  air.  Of  course  this  measured  amount 
must  be  just  so  much  as  can  be  carried  in  one  bucket,  and  every 
stroke  of  the  engine  causes  just  exactly  the  same  amount  of  alcohol 


FIG.  48. 

to  be  fed,  i.e.,  the  contents  of  one  bucket.  Ignition  is  electric,  and 
governing  effected  by  spark  variation  (Chapters  X  to  XII).  The 
double-piston  mechanism  offers  some  interesting  peculiarities  and 
advantages  as  respects  balancing  on  opposite  sides  of  the  crank- 
shaft, and  permits  a  construction  whereby  variable  volumes  of 
clearance  and  compression  become  possible. 

94.  Alcohol-launch  Engine. — It  has  long  been  desired  to 
use  alcohol  instead  of  naphtha  or  gasoline  in  pleasure-launches, 
on  account  of  the  avoidance  of  the  odor  and  the  unquestionably 
greater  safety  of  alcohol  as  a  fuel.  Any  automobile  motor  can  be 
applied  to  launch  uses,  as  the  problem  of  propulsion  on  the  water 
is  usually  less  complicated  than  on  the  land,  by  reason  of  the  prac- 


210  THE   GAS  ENGINE. 

tically  uniform  resistance  offered  by  water.  The  alcohol-launches 
in  America  most  usually  have  condensing  engines  on  account  of 
the  cost  of  alcohol,  and  when  the  apparatus  must  operate  con- 
densing it  is  usually  more  convenient  to  use  the  alcohol  as  a  heat 
medium,  and  by  the  usual  steam-engine  cycle  with  the  heat 
'applied  from  without  or  externally,  and  abandon  the  internal- 
combustion  principle.  In  the  alco- vapor  launches,  for  example, 
alcohol  is  not  burned,  but  the  heat  is  furnished  by  burning  kerosene 
under  a  retort  in  which  the  alcohol  is  vaporized,  and  its  vapor 
tension  drives  the  piston.  In  the  ordinary  naphtha-launches  part 
of  the  naphtha  is  used  in  a  burner  to  vaporize  and  give  tension 
to  that  part  which  drives  the  engine,  operating  in  a  closed  circuit 
or  cycle. 


CHAPTER    IX. 

PROPORTIONING  OF  MIXTURES. 

95.  Introductory.  —  Since  the  internal-combustion  engine 
operates  by  the  oxidation  of  the  fuel  in  the  cylinder,  it  is  of  vital 
importance  that  the  proportion  of  fuel  and  air  should  be  properly 
adjusted  to  each  other  and  to  the  work  to  be  done.  As  the  re- 
sistance on  the  crank-shaft  may  increase  or  decrease  the  supply 
of  fuel  should  increase  or  decrease,  and  the  system  of  governing 
should  be  adjusted  so  as  to  keep  this  mixture  and  the  proportioning 
of  it  at  the  point  of  highest  efficiency.  In  liquid  fuel  this  matter 
is  of  special  consequence,  since  a  drop  of  the  liquid  makes  a  con- 
siderable volume  of  gas  when  vaporized,  and  a  very  small  varia- 
tion in  the  supply  of  liquid  will  make  a  wide  variation  in  the 
supply  of  gas.  It  will  be  seen  in  the  discussion  on  governing 
that  the  proportioning  of  the  mixture  requires  as  careful  attention 
as  the  amount. 

In  the  engine  which  draws  its  supply  of  fuel  from  a  gas-main, 
and  particularly  from  one  which  has  been  divided  and  has  ramified 
through  a  building  or  a  plant,  it  may  easily  happen  that  the  pressure 
in  the  pipe  supplying  the  engine  will  vary  from  day  to  day  or 
from  hour  to  hour.  In  engines  supplied  through  carburetors 
the  speed  of  the  engine  may  easily  produce  a  considerable  differ- 
ence in  the  flow  of  fuel  and  the  proportions  of  the  mixture  due 
to  inertia  of  inlet-valves  or  any  circumstance  which  causes  them 
to  open  sluggishly  or  reluctantly  for  the  inspiration  stroke. 

Where  the  engine  receives  gas  from  a  house-pipe  which  sup- 


212  THE   GAS-ENGINE. 

plies  illuminating  fixtures,  a  further  difficulty  is  to  be  guarded 
against  in  the  fluctuation  of  these  lights  when  the  engine  makes 
its  draught  upon  the  volume  of  gas  in  the  pipe.  Such  fluctuation 
is  not  only  bad  for  the  working  of  the  engine,  but  the  flickering 
of  the  lights  is  disagreeable  and  must  be  prevented.  The  manner 
of  doing  this  in  most  frequent  practice  is  the  introduction  of  a 
chamber  of  variable  volume  close  to  the  engine  on  the  pipe  which 
•supplies  the  gas  to  it.  This  variable  chamber  is  most  frequently 
a  bag  of  flexible  rubber,  which  fills  during  the  three  strokes  during 
which  no  gas  is  withdrawn  and  collapses  partially  when  the 
inspiration  occurs.  If  a  collapsible  rubber  bag  is  inconvenient, 
somewhat  the  same  effect  can  be  produced  by  an  enlargement  of 
the  pipe  so  as  to  form  a  volume  or  storage  space  in  which  the 
elasticity  of  the  gas  itself  shall  act  somewhat  as  the  flexible  rubber 
of  the  bag.  These  enlargements  are  best  arranged  so  that  the 
gas  in  flowing  into  them  comes  in  at  one  end  and  passes  out  at 
the  end  opposite  with  some  distance  between  the  inlet  and  outlet. 
The  enlarged  cross-section  at  once  reduces  the  linear  velocity 
of  the  gas  at  that  end  which  is  towards  the  lines  to  be  affected, 
and  the  withdrawal  by  the  engine  from  the  other  end  does  not 
produce  a  perceptible  pulsation,  where  the  waves  of  such  pulsa- 
tion are  broken  by  so  considerable  a  change  of  cross-section. 

96.  Automatic  Mixing  by  Suction. — The  most  frequent 
method  of  securing  the  desired  proportions  of  gas  and  air  in  the 
gas-engine  is  by  means  of  a  separate  valve  for  air  and  for  gas 
(See  Figs.  28,  29),  the  areas  of  whose  openings  are  adjusted  to 
the  desired  proportion.  When  the  pressure  on  the  working  side 
of  the  piston  is  reduced  by  the  outgoing  stroke,  these  two  valves 
will  lift  automatically  by  the  excess  of  pressure  without,  and 
through  each  of  them  will  stream  the  proper  volume  by  reason 
of  the  difference  of  pressure  below  them  and  above  them.  It 
will  be  apparent,  however,  that  if  either  pressure  varies  (it  is 
usually  the  gas-pressure  which  varies),  the  mixture  will  not  be 
that  for  which  their  areas  have  been  adjusted  and  a  different 
proportion  of  mixture  will  be  the  result.  There  will  be,  usually, 


PROPORTIONING   OF  MIX  TV  RES.  213 

a  cock  in  the  gas- supply  pipe  which  is  supposed  to  be  wide  open 
when  the  engine  is  at  work.  It  is  obvious  that  if  it  is  partly 
closed  a  very  considerable  variation  in  the  proportions  of  the 
mixture  will  prevail,  constantly,  as  long  as  that  condition  lasts. 
If  the  gas  changes  in  quality  or  richness,  a  desirable  change  in 
mixture  can  only  be  reached  by  adjustment  of  that  gas-cock,  if 
the  areas  of  the  valves  are  themselves  unalterable.  The  air- 
valve,  as  a  rule,  is  not  capable  of  adjustment.  It  opens  to  the 
outer  air  or  to  the  air  of  the  room  in  which  the  engine  operates, 
and  there  is  no  way  in  which  it  can  be  increased.  It  may  be 
diminished  if  its  lift  is  controlled  by  a  spring  or  by  a  stop,  but,  in 
general,  the  adjustment  of  the  air-valve  is  not  practised  in  the 
automatic  system.  The  inlet  of  air  is  often  an  occasion  for  noise 
in  the  gas-engine,  since  the  cross- section  of  the  opening  will  of 
necessity  be  usually  much  less  than  that  of  the  piston,  so  that  the 
velocity  of  the  air  through  the  opening  is  many  times  greater  than 
the  linear  velocity  of  the  piston  on  its  inspiration  stroke.  In 
some  forms  of  engine  a  muffler  is  introduced  on  the  inlet  so  as 
to  quiet  the  sound  of  the  air  through  a  constricted  opening. 

The  system  of  mixing  by  automatic  action  is  the  cheapest 
to  construct.  In  its  simple  form  it  attaches  itself  to  governing 
by  the  hit-or-miss  system  (par.  136).  It  has  the  objections  at 
high  speeds  which  apply  to  any  automatically  "operated  valve 
resulting  from  the  delay  in  opening  to  admit  the  incoming  charge 
when  these  valves  have  any  weight  or  mass  or  must  overcome 
the  action  of  the  spring  which  holds  them  shut.  This  system 
is  particularly  unreliable  when  there  is  no  pressure  in  the  tank 
or  vessel  containing  the  fuel.  As  the  speeds  increase  the  mixture 
drawn  in  becomes  less  and  less  rich,  due  to  the  inertia  of  the  fuel 
as  well  as  the  inertia  of  the  valve. 

97.  Proportioning  by  Adjustable  Valves.  —  A  better  system 
of  proportioning  the  mixture  makes  the  inlet  area  both  of  fuel 
and  of  air  controllable.  This  system  appears  in  both  the  Nash 
and  Westinghouse  engines  (Figs.  33.  36),  In  the  Nash  engine 
the  lift  of  the  valve  is  controlled  both  for  gas  and  for  air  to  a 


214  THE   GAS-ENGINE. 

proper  adjustment  of  proportions  as  revealed  by  the  indicator- 
card,  and  the  governor  of  the  hit-or-miss  type  never  varies  the 
proportions  after  they  are  once  adjusted.  In  the  Westinghouse 
engine  the  proportions,  when  once  adjusted,  are  not  varied,  but 
the  governor  acting  on  a  second  valve  draws  in  more  or  less  volume 
of  the  uniform  mixture  as  the  demands  of  the  resistance  may 
require  (Fig  36).  The  proportioning  valve  is  adjusted  experi- 
mentally with  the  indicator  for  the  best  effect  with  the  fuel  and 
pressure  prevailing  at  the  engine.  If  any  change  takes  place  in 
either  quality  or  pressure  of  the  fuel,  the  adjustment  of  the  propor- 
tioning valve  must  be  altered  accordingly.  When  once  correct, 
however,  the  adjustment  need  not  be  changed.  In  the  engines 
which  draw  their  supply  of  air  from  out  of  doors,  as  in  auto- 
mobile practice  the  proportion  of  air  and  fuel  is  more  likely  to  vary 
widely.  There  is  a  greater  weight  belonging  to  a  given  volume 
in  cold  weather  when  the  air  is  dry,  while  in  warm  weather  and 
when  the  air  is  full  of  moisture  there  is  a  corresponding  difference 
in  the  amount  of  oxygen  in  a  given  volume,  which  will  mar  the 
proper  working  of  the  engine  as  the  result  of  variations  in  the 
character  of  the  mixture.  This  system  leaves  much  to  be  de- 
sired. The  logical  outcome  of  this  system  is  governing  by 
throttling  the  mixture  and  not  by  varying  or  impoverishing  it. 

98.  Proportioning  by  Mechanically  Operated  Valves.— By 
reason  of  the  difficulty  referred  to  above  from  the  inertia  or 
sluggishness  in  action  of  automatic  valves  the  tendency  in  high- 
speed practice  in  the  automobile  has  been  distinctly  towards 
mechanically  operated  inlet-valves  which  shall  open  positively 
at  a  definite  point  of  the  stroke  by  means  of  cams  driven  from 
the  half-time  shaft  of  the  motor  (see  Fig.  49).  With  mechani- 
cally operated  valves  governing  must  be  done  by  throttling  the 
amount  of  mixture  which  reaches  the  valve.  The  objection 
to  the  single  mechanically  operated  inlet-valve  which  has  been 
urged  is  that  it  admits  a  charge  of  fuel  to  the  cylinder  at  every 
stroke  whether  the  engine  requires  it  or  not.  This  is  avoided 
in  some  engines  by  the  use  of  two  inlet-valves,  one  for  gas  alone. 


PROPORTIONING  OF  MIXTURES. 


and  the  other  for  the  mixture  (see  Fig.  33). 
of  overcoming  the  resistance  of  the 
valves  by  mechanical  means  in  enabling 
the  cylinder  to  receive  its  full  charge  of 
fuel  at  high  speeds  overbalances  the 
objection  from  this  point  of  view.  It 
may  be  serviceable  to  show  quanti- 
tatively how  considerable  the  suction- 
throttling  may  easily  become.  At  32°  F. 


The  effect,  however, 


fcxha 


FIG.  49. 


and  at  one  atmosphere  pressure  the  volume  of  a  pound  of  air  is 
12.387  cubic  feet  and  it  weighs  .0808  pound  per  cubic  foot. 
At  any  other  pressure  pl  its  volume  vl  will  be 

p0v0     12.387X14-7 


and  the  weight  per  cubic  foot  the  reciprocal  of  this,  or 

A 


12.387X14.7 


•°°55A  pound. 


If  it  be  assumed  that  by  the  sluggishness  of  the  valves  and  air 
due  to  inertia  and  friction  the  pressure  of  the  aspiration  stroke 
is  only  10  pounds  absolute  instead  of  14.7,  then  the  weight  w4 
will  be 

^  =  .005 5X10  =.05 5  pound. 

But  at  atmospheric  pressure  there  should  have  entered  .0808 
pound,  hence  .0808  — .055^.0253  pound  less  went  in  to  fill 

the  volume  generated,  or  a  loss  of  ~~og  =  3I  pei  cent  as  com- 
pared with  that  weight  of  mixture  that  would  have  gone  in  if  the 
speed  had  been  lower,  the  ports  large  enough,  and  the  valves 
effectively  opened  (see  par.  178). 

99.  Proportioning  by  Volumes  of  Pump  Cylinders. — A 
system  of  proportioning  the  charge  by  means  of  separate  pumps 


216  THE   GAS-ENGINE. 

for  air  and  fuel  secures  a  positive  and  continuous  adjustment  of 
their  relative  proportions  when  the  volume  displaced  by  the  piston 
of  each  pump  is  once  fixed.  This  system  is  independent  of 
variations  of  pressure  in  the  gas-mains  and  to  a  great  extent 
independent  of  barometric  pressure  and  atmospheric  tempera- 
ture. This  principle  is  carried  out  in  the  Korting  engine  and 
is  discussed  under  the  method  of  governing  that  engine  (par.  71). 

100.  Proportioning    by    Control    of    the    Carburetor. — The 
design  of  carburetor  can  be  made  to  determine  the  proportions 
of  the  mixture.     This  can  be  done  either  by  varying  the  pro- 
portion of  pure  air  which  meets  the  carbureted  air  in  order  to 
furnish  the  necessary  amount  of  oxygen  for  complete  combus- 
tion, or  the  entire  amount  of  air  may  pass  through  the  carbureting 
appliance  and  the  amount  of  fuel  be   regulated  by  restricting 
its  flow  (see  Chapter  X).     It  is  more  convenient  to  have  the 
proportioning  done  by  the   former  process,   since   under  these 
circumstances  the  only  necessary  adjustment  will  be  for  varia- 
tion in  the  quality  of  the  fuel  due  to  changes  in  its  calorific  value 
and  by  changes  in  the  barometric  or  hygrometric  state  of  the 
air.     When  a  proportion  for  constant  conditions  has  once  been 
established,  the  governing  appliance  will  take  care  of  the  quantity 
of  mixture,  while  the  adjustment  of  the  carburetor  takes  care 
of  the  quality.      -It  is  inconvenient  to  make  the  carburetor  vary 
both  quality  and  quantity  and  to  saddle  the  combined  functions 
upon  the  governing  apparatus.     As  will  be  seen  in  the  treatment 
of  carburetors  in  the  next  chapter,  it   is  quite   easy  to  adjust 
the  proportion  of  liquid  fuel  when  the  suction  effect  is  practically 
constant  so  as  to  make  the  desired  mixture. 

101.  Effect  of  Scavenging. — It  has  already  been  foreshadowed 
in  a  previous  paragraph  (No.  75)  that  methods  have  been  de- 
signed to  cleanse  the  cylinder  from  burnt  products  of  combus- 
tion by  providing  for  a  scavenging  effect  by  means  of  pure  air. 
The  effect   of  this   scavenging  stroke   is  to  relieve  the  cylinder 
and  the  combustion-chamber  of  gases  which  are  not  supporters 
of  combustion,  so  that  when  the  fresh  mixture  came  in  it  should 


PROPORTIONING   OF  MIXTURES.  217 

not  become  diluted  by  being  mixed  with  exhaust-gases  which 
were  not  combustible. 

It  is  apparent,  therefore,  that  any  device  in  the  design  of 
the  engine  which  shall  produce  an  effect  the  reverse  of  scavenging 
will  produce  a  material  variation  in  the  composition  of  the  mix- 
ture whose  ignition  performs  the  working  stroke.  Those  methods 
of  governing  which  preclose  the  exhaust-valve  before  the  stroke 
is  ended  leave  a  residue  of  such  incombustible  gases  in  the  cylinder. 
This  residue  not  only  prevents  the  inlet  of  the  same  quantity  of 
new  mixture  on  the  inspiration  stroke  as  would  enter  if  the  com- 
bustion-chamber had  been  completely  emptied,  but  by  their 
presence  in  the  mixture  they  retard  the  rapidity  with  which  the 
combustion  takes  place  in  the  fresh  mixture;  their  heat  lowers 
the  density  of  the  charge  and  therefore  diminishes  the  intensity  of 
the  initial  pressure  and  the  average  or  mean  pressure  throughout 
the  working  stroke. 

It  will  be  apparent,  therefore,  that  the  effect  of  these  gases 
when  the  governor  uses  them  as  a  means  of  controlling  speed 
is  twofold.  They  act  to  diminish  the  quantity  of  combustible 
and  to  modify  its  normal  behavior  after  ignition.  It  is  the  latter 
effect  which  is  the  element  of  uncertainty  in  the  proportioning 
of  the  mixture  with  this  system. 

102.  Effect  of  Variations  in  the  Mixture. — The  principal 
effect  of  variations  in  composition  of  the  explosive  mixture  is 
upon,  the  rapidity  with  which  the  flame  propagates  itself  through- 
out the  combustion-chamber.  Experiment  has  shown  that  there 
is  a  proportion  at  which  the  pressure  at  the  beginning  of  the 
stroke  caused  by  the  inflammation  of  the  mixture  rises  most 
rapidly  and  produces  the  greatest  effect  (see  Chapter  XIX).  To 
impoverish  this  mixture  by  diminishing  the  proportion  of  fuel 
in  it  retards  the  ignition  process,  diminishes  the  initial  pressure, 
lowers  the  average  or  mean  pressure  through  the  forward  stroke, 
and  may,  perhaps,  be  carried  to  a  point  at  which  ignition  will 
not  occur  at  all.  At  or  near  the  limit  of  such  impoverishment 
it  will  be  apparent  that  variations  in  the  amount  of  the  com- 


2i 8  THE  GAS-ENGINE. 

pression  on  the  return  stroke  will  vary  the  readiness  of  the  mixture 
to  ignite.  Where  the  impoverished  mixture  is  also  throttled, 
it  may  result  that  on  the  return  or  compression  stroke  the  com- 
pression may  not  reach  a  point  at  which  that  particular  mixture 
would  ignite  at  all,  whereas  a  richer  mixture  or  a  higher  com- 
pression would  both  of  them  favor  such  ignition  and  cause  it  to 
take  place.  An  impoverished  mixture,  furthermore,  and  partic- 
ularly one  which  is  diluted  with  products  of  combustion,  may 
ignite  slowly  enough  so  that  it  is  not  completely  burned  at  the 
time  when  the  exhaust-valves  should  open  at  the  beginning  of 
the  return  stroke.  This  state  of  affairs  is  particularly  annoying 
with  the  two-cycle  type  of  engine,  since  the  incoming  charge  of 
fresh  combustible  mixture  is  expected  to  follow  the  discharge 
of  the  products  of  combustion.  If  the  latter  are  flaming  after 
the  exhaust-valve  is  opened,  they  will  ignite  the  incoming  mixture, 
and  usually  that  ignition  will  run  back  into  the  crank-case  or 
other  end  of  the  cylinder,  setting  fire  to  the  charges  of  mixture  in 
that  space,  which  will  result,  of  course,  in  the  stoppage  of  the 
engine.  Retarded  ignition  which  continues  into  the  exhaust- 
pipe  will  obviously  make  the  latter  excessively  hot. 

It  is  apparent,  furthermore,  that  indeterminate  variations 
of  the  mixture  render  it  difficult  or  impossible  to  regulate  the 
engine  closely  to  a  predetermined  speed.  If  the  mechanical 
appliances  for  regulation,  acting  according  to  law,  produce  their 
effects  upon  a  mixture , which  is  not  determined  by  law,  an  un- 
certainty in  regulation  is  at  once  unavoidable.  If  the  mixture 
is  varied,  it  should  be  varied,  in  a  determinate  way. 

103.  Effect  of  Speed  Variations  in  Varying  the  Mixture. — 
With  engines  working  upon  gaseous  fuel,  the  effects  of  variation 
in  speed,  and  particularly  the  effects  of  high  speed,  are  not  apparent 
in  producing  wide  variations  in  the  proportions  of  their  mixture. 
In  the  engines  which  carburate  the  air  by  a  liquid  fuel,  the  effect 
of  speed  variations  and  high  speed  in  varying  the  mixture  will 
usually  be  considerable.  If  the  liquid  fuel  is  inspirated  into  a 
current  of  air,  the  pressure  which  causes  that  inspiration  of  liquid 


PROPORTIONING   OF  MIXTURES.  219 

will  be  greater  when  the  speed  of  such  inspiration  is  higher. 
There  will  result,  therefore,  that  the  mixture  will  be  richer  from 
the  action  of  this  cause  when  the  speed  is  high  than  when  the 
speed  is  low. 

On  the  other  hand,  if  the  inlet-valves  of  the  engine  are  operated 
automatically  by  differences  of  pressure  inside  the  cylinder  on 
the  inspiration  stroke,  as  compared  with  the  pressure  of  the 
external  air,  the  inertia  of  these  valves,  and  of  the  column  of  air 
in  the  pipe  and  of  the  liquid  to  be  inspirated  into  the  column  of 
air  have  to  be  overcome  by  that  difference  of  pressure;  and  if 
the  time  of  the  inspiration  stroke  varies  as  the  speed  of  the  engine 
varies,  it  will  be  obvious  that  carburated  air  will  flow  into  the 
cylinder  through  a  less  proportion  of  the  inspiration  stroke  at 
high  speed  than  when  the  period  of  that  stroke  is  longer.  If,  on 
the  other  hand,  the  valves  are  mechanically  operated,  the  inertia 
of  the  valves  is  eliminated  from  the  problem,  but  only  the 
inertia  of  the  air  and  liquid  remain.  For  these  reasons  the 
mechanically  operated  inlet-valves  cause  a  less  wide  variation  in 
the  mixture  than  is  certain  to  occur  with  the  automatic  system 
of  inlet-valves. 

It  may  easily  occur  with  the  automatic  system  that  a  speed 
should  be  reached  at  which  the  inertia  of  the  flow  of  mixture, 
together  with  friction  in  pipes,  bends,  and  valves,  may  result 
in  a  relatively  small  proportion  of  mixture  reaching  the  cylinder 
(par.  98).  On  the  return  of  the  piston  the  compression  will  be 
less,  and  the  less  volume  of  fuel  will  make  the  next  working 
stroke  a  weaker  one  as  the  result  of  both  effects.  Barometric 
pressure  of  the  external  air  will  obviously  influence  the  response 
of  the  air  in  the  pipes  to  the  differences  of  pressure  inside  the 
cylinder  and  out.  If  the  air  is  cool  and  dry,  it  weighs  more  to 
the  cubic  foot  than  when  the  air  is  warm  and  moist.  These 
causes  produce  as  their  effect  the  curious  phenomenon  of  a 
diminishing  horse-power  in  the  motor  with  increase  of  its  speed 
of  revolution.  This  is  a  condition  which  is  practically  unknown 
in  engines  of  the  constant-pressure  class,  such  as  the  steam-engine 


220  THE  GAS-ENGINE. 

receiving  energy  in  the  form  of  a  gas  under  pressure  from  a 
reservoir.  As  in  the  previous  case,  this  variation  of  speed  may 
be  both  in  quantity  and  in  quality,  with  carburated  mixtures, 
since  the  inertia  of  the  liquid  will  be  different  from  that  of  the 
air,  and  the  effects  of  speed  on  such  inertia  will  be  different. 

If,  from  any  circumstance,  the  mixture  becomes  too  rich  in 
fuel,  the  combustion  will  be  probably  incomplete  within  the  cylin- 
der, and  the  exhaust  will  have  an  offensive  odor  from  partly  burned 
and  partly  carbonized  fuel.  This  state  of  affairs  will  reveal 
itself  also  by  the  presence  of  visible  vapor  resembling  smoke  in 
the  otherwise  colorless  exhaust-gases. 

Obviously,  also,  defective  proportioning  of  this  sort  consumes 
an  unnecessary  or  wasteful  amount  of  fuel. 


CHAPTER  X. 

CARBURATION  AND  CARBURETORS. 

105.  Introductory. — In  cities  and  els 2 where  the  stationary 
internal-combustion  engine  may  receive  its  supply  of  hydro- 
carbon for  use  as  fuel  in  the  form  of  gas  from  a  central  generat- 
ing station.  This  gas  distributed  through  mains  and  pipes  is 
ready  for  use  as  received.  When  the  plant  using  gas-engines  is 
a  large  one  the  necessary  gas  supply  can  be  more  cheaply  sup- 
plied from  an  independent  producer  (pars.  24-28). 

In  small  isolated  plants,  such  as  the  automobile  and  the  launch 
for  marine  purposes,  it  is  convenient  to  make  use  of  the  hydro- 
carbon in  liquid  form.  It  can  be  carried  conveniently  in  tanks 
and  supplied  to  the  engine  as  required,  and  is  consumed  in  the 
form  in  which  it  is  bought  and  sold  in  the  market. 

The  use  of  the  liquid  hydrocarbon,  however,  will  necessitate 
an  apparatus  whereby  the  gas  can  be  manufactured  from  the 
liquid  fuel  as  required  by  the  engine.  The  most  convenient 
form  of  gas  for  engines,  perhaps,  will  be  that  which  is  made  by 
carburating  atmospheric  air  as  described  in  paragraph  22.  One 
of  the  great  steps  in  the  development  of  the  modern  internal- 
combustion  engine  has  been  the  design  of  satisfactory  apparatus 
to  carburate  air  just  before  it  enters  into  the  combustion-chamber. 
The  idea  of  carburation  is  not  a  new  one,  but  the  improvement 
in  the  forms  which  have  been  produced  for  the  purpose  has 
drawn  a  distinct  line  between  the  early  and  the  more  modern 
forms.  In  fact  it  is  not  too  much  to  say  that  the  successful 
working  of  the  automobile  engine  and  of  all  other  engines  of  the 


221 


222  THE  GAS-ENGINE. 

same  class  is  principally  dependent  upon  the  certainty,  reliability, 
and  satisfactory  working  of  the  carburating  device. 

The  carburating  apparatus  will  serve  to  saturate  atmospheric 
air  with  any  liquid  hydrocarbon.  There  will,  therefore,  be 
carburetors  for  gasoline,  for  kerosene  and  for  alcohol,  divided 
only  as  required  by  the  varying  characteristics  of  the  liquid.  In 
general  the  process  of  carburation  is  to  saturate  the  atmospheric 
air  with  the  liquid  fuel  in  a  finely  divided  or  atomized  state  like 
a  mist.  This  general  principle  of  atomization  has  long  been  used 
in  medicine  and  surgery  and  is  familiar  in  the  form  of  the  apparatus 
used  in  spraying  perfumes.  The  air  saturated  with  a  mist  of 
hydrocarbon  will  subsequently  undergo  a  further  mixture  with 
an  additional  supply  of  air  such  as  may  be  required  for  its  full 
and  complete  combustion  in  the  working  cylinder.  With  the 
less  volatile  hydrocarbons  the  process  of  carburating  the  air 
cannot  be  satisfactorily  carried  on  at  the  ordinary  temperatures 
of  the  external  air.  The  carburetor  for  such  liquids  will  have 
both  the  principle  of  atomization  and  the  subsequent  vaporiza- 
tion by  heat.  When  the  engine  is  working,  the  vaporization  can 
be  effected  by  waste  heat  from  the  hot  exhaust-gas.  In  starting 
the  motor,  however,  when  all  is  cold,  the  vaporization  requires 
an  outside  source  of  heat  in  lamp  or  torch  or  otherwise. 

The  first  principle  in  carburation,  historically,  is  the  evapo- 
ration of  the  volatile  hydrocarbon  at  atmospheric  temperatures, 
from  the  surface  of  its  own  liquid.  Such  carburation  may  be 
called  surface  carburation,  and  the  evaporation  may  then  be  from 
the  cool  surface,  or  the  volatility  of  the  liquid  may  be  increased 
by  heating.  This  system  requires  that  a  current  of  air  to  be 
carburated  moves  over  the  surface  of  the  liquid. 

The  second  system  may  be  called  the  principle  of  mechanical 
ebullition.  The  current  of  air  to  be  saturated  is  made  to  pass 
through  the  liquid  mass,  so  that  it  bubbles  up  through  the  liquid 
and  escapes  at  the  surface.  By  this  bubbling  the  liquid  is 
mechanically  agitated  and  a  certain  proportion  of  it  is  entrained 
with  the  air  in  a  finely  divided  state  or  mist. 


CARBURATION  AND  CARBURETORS.  223 

The  third  principle  is  that  of  the  spray  carburetor.  These 
are  true  atomizers  in  which  the  jet  of  liquid  fuel  "s  thrown  up 
into  the  current  of  moving  air  by  the  fact  that  the  air  on  its  way 
to  the  cylinder  on  the  aspirating  stroke  of  the  engine  has  a  pressure 
less  than  atmosphere.  A  small  orifice  or  nozzle  opening  into 
the  suction-pipe  delivers  the  liquid  fuel  into  that  moving  current, 
and  by  the  mechanical  action  of  this  current  the  mist  or  cloud 
of  liquid  particles  is  distributed  through  the  moving  current 
which  it  saturates. 

It  will  be  seen  in  the  later  treatment  that  the  form  of  the 
apparatus  utilizing  this  third  principle  for  the  less  volatile  hydro- 
carbons will  require  that  the  spray  be  made  into  a  gas  by  heat. 
With  gasoline,  as  a  rule,  it  is  not  necessary  to  vaporize  the  mist. 
The  first  two  principles  are  practically  out  of  competition  with 
the  third,  which  is  the  modern  form. 

1 06.  The  Surface  Carburetor.  The  De  Dion  Motor-cycle 
Type. — One  of  the  earliest  forms  of  the  surface  carbureter  was 


FIG.  53- 

brought  out  for  the  early  motor  cycles  and  is  illustrated  in  Figs.  53 
and  54.     The  liquid  gasoline  is  poured  into  the  containing  vessel 


224 


THE  GAS-ENGINE. 


and  lies  in  the  lower  part.  The  current  of  external  air  is  drawn 
down  through  the  inlet  /  so  that  underneath  the  plate  L  it  spreads 
itself  over  the  surface  of  the  gasoline  and  picks  up  the  vapor 
which  rises  to  the  surface.  The  level  of  the  plate  L  can  be  ad- 
justed as  the  level  of  the  liquid  varies.  It  acts  both  as  a  spatter- 
plate  and  to  discharge  the  air  in  an  even  volume  over  the  surface. 
The  volatility  of  the  gasoline  may  be  increased  by  passing  hot 
exhaust-gas  through  the  tube  A  and  out  into  the  exhaust-pipe 
at  H.  The  carburated  air  rises  at  the  top  of  the  carburetor 
through  the  opening  B  into  the  chamber  K,  which  is  known  as 


FIG.  54. 

the  twin  tap  from  its  construction  as  shown  in  Fig.  54.  The 
carburated  air  from  the  carburetor  meets  an  additional  supply 
of  air  from  outside  through  D,  which  is  protected  by  a  wire 
cage  and  can  be  controlled  in  area  by  means  of  the  lever  G. 
This  control  can  be  made  to  vary  the  proportion  of  fuel  and 
air  which  passes  through  .the  passage  R  into  the  pipe  E,  which 
delivers  the  mixture  in  explosive  proportions  to  the  engine  cyl- 
inder. The  lever  G7  is,  therefore,  a  throttle  lever  varying  the 


CARBURATION  AND   CARBURETORS. 


22$ 


amount  of  mixture  delivered  to  the  cylinder,  while  the  lever  G 
varies  the  proportions  of  air  and  fuel  in  the  mixture.  That  is, 
G  regulates  the  quality  and  G'  regulates  the  quantity. 

107.  Wick  or  Flannel  Carburetors. — Belonging  to  this  same 
type  and  form,  the  second  class  are  the  carburetors  which  are 
known  as  the  felt  or  flannel  type,  of  which  Fig.  55  will  serve  as 


FIG.  55- 

an  illustration.  The  air  is  drawn  in  by  suction  of  the  engine 
stroke  through  the  pipe  e  and  enters  at  v,  so  that  a  pressure  less 
than  the  atmosphere  is  created  in  the  carburating-chamber.  The 
carburetor  is  made  of  thin  metal  and  is  divided  into  a  spiral  by  a 
thin  metal  coil  which  is  fast  to  the  top  of  the  carbureter,  but  does 
not  extend  all  the  way  to  the  bottom.  It  will  be  plain,  therefore, 
that  when  the  carbureter  is  filled  half  full  of  gasoline,  as  to  the 
level  of  the  line  xy,  for  example,  the  atmospheric  air  which  enters 
through  the  opening  of  the  valve  v  will  be  compelled  by  the  spiral 
to  pass  around  the  coil  in  order  to  reach  the  central  outlet  and 


226 


THE   GAS-ENGINE. 


be  discharged  through  the  pipe  e.  The  surface  of  the  spiral  coil 
is  covered  with  felt  or  flannel  loosely  stretched  on  the  thin  metal 
by  basting  it  through  holes  made  for  the  purpose.  This  felt  or 
flannel  reaching  down  into  the  gasoline  draws  up  the  liquid  by 
capillary  action,  and  the  passage  of  the  air- current  over  the  wick 
surface  evaporates  off  the  liquid  and  thus  saturates  the  air. 

In  surface  or  wick  carburetors  of  this  type  experience  shows 
that  the  best  results  are  secured  when  about  four  inches  of  liquid 
lie  in  the  bottom  of  a  carburetor  about  eight  inches  deep. 


FIG.  56. 

In  another  form  of  wick  or  surface  type  (the  Bray  ton,  Fig.  56) 
the  space  b  is  filled  with  sponge  or  felt  or  some  material  of  simi- 
lar sort.  The  liquid  hydrocarbon  enters  at  the  top  through  the 
pipe  e,  while  a  jet  of  air  is  forced  through  the  pipe  /,  serving  to 
atomize  or  spray  the  liquid.  The  additional  air  necessary  lor 
the  complete  combustion  enters  through  the  pipe  o  and  passes 
through  the  porous  bed  b,  when  the  valve  5  is  opened.  The  cut 
shows  this  form  of  carburetor  applied  directly  to  the  engine  cyl- 


CARBURATION  AND  CARBURETORS. 


227 


inder.     The  opening  closed  by  the  plug  g  is  provided  to  receive 
a  taper  to  effect  the  ignition  in  starting  the  engine.* 

The  objection  to  the  flannel  or  wick  carburetor  for  out-of-door 
use  has  been  the  gradual  fouling  of  the  fibres  of  the  wick  with: 
dust,  so  that  on  becoming  clogged  they  would  no  longer  serve 
as  an  evaporating  surface.  The  objections  to  the  De  Dion  form 
of  evaporation  directly  from  the  surface  of  the  mass  were  that 
the  process  of  vaporization  requires  a  certain  amount  of  heat 

FIG.  57. 


which  ¥/as  naturally  absent  from  the  liquid  mass.  It  gradually, 
therefore,  became  chilled  and  frozen,  or  in  any  case  lost  its 
readiness  to  give  off  its  volatile  components  as  the  temperature 
lowered.  Furthermore,  as  the  volatile  elements  were  naturally 
drawn  off  first,  the  mixture  became  less  and  less  volatile,  until 
finally  its  capacity  for  saturating  air  at  atmospheric  temperatures 
disappears  entirely  by  the  continued  process  of  fractional  distil- 
lation at  atmospheric  temperatures. 

Figs.  57  and  58  show  a  form  of  wick  or  flannel  carburetor  in 

*  For  the  privilege  of  using  Figs.  55  and  56  in  their  present  form,  as  repro- 
duced from  patent  drawings,  the  author  is  indebted  to  the  International  Text- 
book Co.  of  Scranton,  Pa. 


228 


THE  GAS-ENGINE. 


which  the  current  of  air  is  made  to  traverse  a  considerable  length 
of  porous  surface  by  the  construction  of  baffle-plates  attached 
alternately  to  the  opposite  sides  of  the  vessel  and  reaching  nearly 
across.  The  air  enters  into  the  first  compartment  c  and,  after 
passing  from  side  to  side  over  the  felt  surface  which  is  moistened 
by  the  gasoline,  it  passes  outward  through  the  pipe  /  through  q. 

108.  Carburation  from  a  Gauze  Surface.  Olds  Type. — To 
avoid  the  inconvenience  from  a  fibrous  or  porous  material  and 
yet  secure  the  convenient  vaporization  from  the  gasoline  surface 
the  type  of  carburetor  used  in  the  Olds 
motor  offers  some  distinct  advantage. 
As  presented  in  Fig.  59,  the  supply  of  air 
from  without  enters  from  the  right.  The 
supply  of  liquid  fuel  is  delivered  through 
the  pipe  N  under  slight  pressure  to  the 
interior  of  the  conical  tube  of  light  wire 
gauze.  The  air  passing  around  this 
moistened  gauze  surface  picks  up  the 
required  amount  of  fuel  and  passes 

through  the  throttle-valve  V  to  the  engine.  Any  liquid  which 
the  air  does  not  absorb  runs  down  through  the  conical  tube  and 
is  delivered  back  to  the  supply-tank.  Fig.  60  shows  the  con- 


FIG.  60. 


struction  of  the  carburetor  system  -complete.  A  small  leather 
diaphragm  at  A  has  upon  its  surface  a  varying  pressure  resulting 
from  the  pulsations  caused  by  the  trunk  of  the  engine  in  the 


CARBURATION  AND   CARBURETORS. 


229 


closed  crank-case.  It  therefore  acts  as  an  air-pressure  pump,  lift- 
ing fuel  to  B.  From  here  it  circulates  through  the  carburetor 
proper  C,  and  any  unused  excess  goes  back  to  the  bottom  of  the 
fuel-tank. 

109.  Carburation  by  Mechanical  Ebullition. — In  the  early 
Daimler  cycles  and  motor  cars  the  form  of  carburetor  devised 
by  Gottlieb  Daimler  was  used,  which  is  shown  in 
Fig.  61.  In  the  cylindrical  vessel  containing 
gasoline  was  placed  a  hollow  float.  The  entering 
air  came  down  through  the  central  tube,  which 
was  borne  by  the  float  so  that  there  should  be  a 
constant  immersion  of  the  lower  end  of  that  tube 
below  the  surface  of  the  liquid.  As  the  engine 
made  its  aspirating  stroke  air  was  drawn  in  both 
through  the  top  of  the  smaller  cylinder  and  through 
the  central  tube.  The  air  which  passed  through 
the  gasoline  became  carburated  and,  uniting  with 
the  air  from  without,  passed  to  the  engine  cylinder 
in  explosive  proportions. 

The  objections  to  this  system  were  the  same 
as  those  attached  to  the  De  Dion  type  as  far  as  the 
FIG.  61.         lowering  of  temperature  and  the  fractional  dis- 
tillation are  concerned. 

no.  Spray  Carburetors.  Float-feed  Type.  Maybach's. — The 
third  principle  in  carburation  which  involves  the  spraying 
action  of  the  liquid  fuel  into  the  current  of  air  is  the  modern 
system.  It  appears  in  two  general  forms.  In  the  one  the  level 
of  the  gasoline  in  the  tank  or  chamber  which  supplies  the  spraying 
jet  is  kept  at  a  constant  level  a  little  below  that  of  the  nozzle,  so 
that  the  reduction  of  pressure  causes  the  flow  of  liquid.  When 
the  aspiration  ceases  the  flow  ceases  without  the  intervention  of 
a  valve  whose  closure  shuts  off  the  delivery  of  fuel.  In  the  second 
type  the  flow  of  fuel  is  checked  by  the  closure  of  a  valve,  and 
therefore  no  float  is  required  to  maintain  a  constant  level  with 
respect  to  the  orifice  of  the  jet. 


23° 


THE  GAS-ENGINE. 


One  of  the  earliest  of  the  float  carburetors  was  that  of  William 
Maybach,  a  colleague  of  Daimler,  which  is  shown  in  Fig.  62. 
The  gasoline  is  delivered  by  gravity  or  pressure  into  the  top  of 
the  chamber  at  the  right  through  the  opening  which  is  controlled 
by  a  needle- valve  attached  to  the  float  A.  As  the  float  falls  the 
supply  of  liquid  is  permitted  to  rise,  and  as  it  rises  the  opening 
is  closed.  The  bottom  of  the  float-chamber  is  connected  to 
the  carburetor  proper  through  the  pipe  B.  The  air  enters  upon 
the  aspirating  stroke  when 
the  valve  D  is  opened, 
whereby  the  pressure  in 
the  mixing  -  chamber  is 
made  less  than  atmos- 
phere, so  that  the  liquid 
fuel  rises  through  the 
capillary  orifice  by  excess 
of  pressure  and  mixes  with 
the  air  in  C.  It  will  be 
apparent  that  no  valve  is 
necessary  except  the  one 
controlled  by  the  float,  and  the  fuel  will  only  enter  the  mixing- 
chamber  C  as  required,  with  the  pressure  variation  upon  the 
suction  stroke  of  the  motor.  The  more  complicated  forms  of 
float  carburetors  are  really  all  derivatives  of  the  simple  Maybach 
type.  Some  illustrative  types  may  be  useful. 

in.  Float  Carburetor  Constant  Level.  Distributing  Cone. 
The  Phoenix-Daimler,  and  Longuemare* — The  float  in  the 
chamber  with  the  needle-valve  attached  directly  to  it  was  found 
to  offer  some  inconvenience  when  applied  to  the  motor  vehicle 
exposed  to  jolts.  The  needle-valve  would  be  opened  by  the 
inertia  of  the  float,  even  when  the  chamber  was  full  enough  to 
close  the  valve  when  the  carburetor  stood  still.  It  was,  there- 
fore, a  simple  modification  to  separate  the  float  from  the  needle- 
valve  and  to  cause  the  latter  to  be  held  shut  by  counterweight 
levers,  whose  action  should  be  overcome  by  the  float  when  the 


FIG.  62. 


CARBURATION  AND   CARBURETORS. 


231 


level  fell.     The  form  of  carburetor  shown  in  Fig.  63  illustrates 
the  counter-weighted  spindle,  and  in  addition  the  plan  of  making 


FIG.  63. 


FIG.  64. 

the  jet  of  gasoline  to  impinge  upon  a  conical  surface  where  it 
should  be  spread  in  a  thin  film  over  which  the  incoming  air  must 
pass. 

The  Longuemare  carburetor,  shown  in  Fig.  64,  illustrates  the 


*32  THE   GAS-ENGINE. 

same  type  of  float  and  counterweighted  levers  for  the  needle- 
valve  and  the  same  principle  of  baffling  the  flow  of  liquid  fuel. 
The  gasoline  enters  at  the  inlet  /  at  the  lower  left  hand  and  is 
discharged  through  the  nozzle  which  is  controlled  by  the  valve  L. 
The  .air  enters  from  without  at  X,  and  the  mixture  passes  to  the 
engine  through  the  connection  F.  The  valve  L  controls  the  size 
of  the  fuel- jet,  and  by  means  of  the  handle  S  the  proportion  of 
air  which  the  gasoline  saturates  is  controlled  by  means  of  the  lift 
of  the  check-valve.  The  additional  supply  of  air  which  does  not 
undergo  saturation  passes  around  through  the  space  P  to  form 
the  explosive  mixture.  This  form  of  carburetor  is  fitted  with  the 
heat-jacket  V  within  which  the  hot  products  of  combustion  may 
circulate  if  desired.  For  starting  the  carburetor  with  the  more 
reluctant  liquids  the  hollow  jacket  can  be  packed  with  cotton 
or  similar  material  soaked  with  liquid  fuel  and  then  ignited. 
The  openings  c  permit  the  flow  of  air  for  combustion  until  there 
shall  be  a  flow  of  hot  gas.  At  d  are  wings  of  thin  metal  which 
are  intended  to  grow  hot  and  to  serve  as  vaporizers  in  addition 
to  the  carburetor  effect  below. 

112.  Float  Carburetor.     Constant  Level  with  Baffle-plates. 
— Fig.  65  shows  a  type  of  carburetor  intended  to  compel  the 
intimate  mixture  of  the  mist  of  fuel  with  the  incoming  air.     At 
the  right  is  the  float-chamber  which  supplies  the  liquid  fuel  to  a 
diffusing  orifice  in  the  carburetor  proper.     The  air  entering  from 
below  is  forced  by  baffle-plates  to  take  a  circuitous  course  over 
the  surface  of  these  plates,  from  which  it  takes  up  any  liquid 
which  may  have  run  down  by  gravity  from  the  diffusing  orifice. 
The  initial  supply  of  air  comes  in  with  the  gasoline  through  the 
ball  valve  between  the  two  chambers,  and  the  passage  between 
these  chambers  can  be  closed  by  the  needle- valve  from  without. 
This  form  of  carbureter  has  an  interesting  detail  by  using  the 
glass  front  through  which  the  operation  of  the  diffusing  appliance 
can  be  observed. 

113.  Carburetors  without  Floats. — In  the  third  class  of  car- 
buretors, in  which  the  jet  of  gasoline  enters  the  incoming  air 


CARBURATION  AND  CARBURETORS. 


233 


through  the  valve  or  other  appliance  actuated  by  the  air,  its 
apparent  simplicity  is  secured  by  doing  away  with  the  float  and 
its  attachments.  It  will  be  apparent  by  the  study  of  the  Longue- 
mare  design  of  carburetor  that  it  consists  of  a  number  of  parts 


FIG.  65. 

which  make  it  costly.  The  float  principle,  furthermore,  is 
liable  to  derangement  by  jolts  or  jars  in  a  moving  vehicle  on  a 
rough  road. 

In  the  form  of  carburetor  shown  in  Fig.  66,  which  is  known 


FIG.  66. 


as  the  James-Lunkenheimer  design,  the  air  enters  from  below 
through  the  inlet  H.    The  cylinder  is  connected  to  the  side 


234 


THE  GAS-ENGINE. 


inlet  /,  so  that  when  the  piston  make  its  aspirating  stroke  the 
pressure  from  without  overcomes  he  pressure  of  the  spring 
which  holds  down  the  valve  B.  The  gasoline  enters  through 
the  pipe  /,  which  supplies  the  channel  G  in  the  casing  of  the  valve, 
from  which  the  necessary  number  of  outlets  open  into  the  seat, 
which  is  closed  by  the  valve  B.  It  will  be  apparent,  therefore, 
that  when  the  valve  lifts  by  the  lowering  of  the  pressure  upon  it, 
it  opens  the  gasoline  passages  and  the  liquid  fuel  enters  at  various 
points  in  the  annular  air-current  moving  past  the  valve.  When 
the  valve  shuts,  both  the  gasoline  and  the  air  supply  are  shut  off 
at  once.  The  opening  from  the  gasoline-pipe  /  is  controlled  at 
will  by  the  needle- valve,  which  has  a  milled  head  E  and  an  indi- 
cator and  locking  device  whereby  it  can  be  set  once  for  all  for 
any  desired  fuel-supply.  The  lift  of  the  valve  is  also  controllable 
by  the  stop  which  is  adjustable  by  the  milled  head  L. 

Another  form  involving  much  the  same  principle  is  illustrated 
hi  Fig.  67.      The  air  enters  from  above  through  the  openings 

a,  and  the  gasoline  is  supplied 
through  the  pipe  E.  The  valve 
in  the  gasoline-pipe  is  held  upward 
by  the  spring  so  that  its  normal 
position  is  closed.  When  the  motor 
aspirates,  the  piston  on  the  valve- 
spindle  is  lowered,  compressing  the 
spring  and  opening  the  gasoline- 
valve  at  the  same  time  that  the  pas- 
sage A  to  the  cylinder  is  opened  by 
the  air-pressure  on  the  top  of  the 
carburetor  piston.  At  the  end  of  the 
charging  stroke  the  spring  forces 
the  piston  up,  closing  the  valve  and 
shutting  off  the  access  of  air.  This 
design  shows  also  the  jacketing  of 
FIG.  67.  the  carbureter  by  the  hot  products 

of  combustion  surrounding  this  upper  part  and  entering  through 


CARBURATION  AND  CARBURETORS.  235 

the  upper  nozzle  at  the  right  hand.  The  carburetors  in  use  on 
the  majority  of  the  American  automobile  motors  belong  to  this 
third  class  and  are  made  by  the  builders  of  the  engine  themselves 
under  license  from  the  basal  patent  illustrated  in  Fig.  66.  The 
objections  to  the  principle  are  met  in  the  high-speed  types  of 
motor  which  operate  with  wide  variations  in  the  load.  The 
difficulty  with  the  high-speed  requirement  is  due  to  the  inertia 
of  the  inlet-valve  and  the  resistance  offered  by  the  spring.  At 
high  speeds  the  actuating  pressure  caused  by  the  motor  piston 
is  applied  so  rapidly  that  the  interval  occupied  by  the  entire 
charging  stroke  becomes  so  short  that  the  inertia  of  the  valve  and 
the  resistance  of  the  spring  retard  the  opening  of  the  valve  until 
the  motor  piston  has  traversed  a  considerable  fraction  of  its  stroke. 
In  consequence  the  volume  of  the  motor  cylinder  is  not  filled  with 
the  weight  of  combustible  charge  which  would  enter  at  atmos- 
pheric pressure  if  the  engine  were  moving  slowly  (see  par.  98). 
The  diminished  weight  of  charge  or  the  less  mass  in  the  motor 
cylinder  results  in  a  diminished  compression  and  in  the  presence 
of  a  less  amount  of  explosive  energy  and  in  a  less  initial  pressure 
over  the  working  stroke.  It  follows,  therefore,  that  the  horse- 
power of  the  motor  supplied  with  a  carburetor  of  this  class  may 
not  necessarily  increase  with  the  number  of  revolutions  as  com- 
putation would  require.  The  horse-power  will  increase  with 
the  speed  up  to  a  point  which  may  be  called  the  critical  speed 
of  the  motor;  and  beyond  that  the  increase  of  speed  is  followed 
by  decrease  of  mean  pressure  propelling  the  piston,  so  that  the 
motor  has  a  limit  of  its  capacity  set  by  this  condition  and  it  does 
not  become  more  powerful  by  increasing  its  speed.  The  difficulty 
set  by  variable  resistance  results  from  the  fact  that  the  flow  of 
gasoline  is  determined  by  the  adjustment  of  the  valve  which 
corresponds  to  E  in  Fig.  66  and  which  it  is  not  convenient  to 
adjust  for  the  variations  of  the  load.  This  is  the  case  if  the 
gasoline  is  supplied  by  gravity  or  under  a  constant  head  through 
the  opening  G.  Too  much  fuel  will  come  in  when  the  valve  is 
open  for  a  considerable  interval  when  an  engine  is  moving  slowly, 


236 


THE   GAS-ENGINE. 


and  not  enough  may  pass  during  the  very  short  interval  when 
the  engine  is  working  rapidly.  On  the  other  hand,  with  engines 
of  high  speed  and  a  certain  adjustment  of  the  spring  it  may 
easily  happen  that  the  valve  hardly  ever  closes  down  tight  upon 
its  seat,  but  hangs  suspended  in  the  continual  flow  of  air  which 
in  a  multiple-cylinder  engine  is  practically  continuous  with  the 
pulsations  hardly  noticeable.  In  such  a  case  the  adjustment  of 
the  valve  E  if  correctly  made  may  cause  the  motor  to  work  satis- 
factorily even  under  variations  of  resistance. 

Belonging  in  the  same  general  group  as  to  operation  to  which 
the  floatless  carbureter  belongs  may  be  grouped  certain  other 

forms  in  which  the  float  is  used. 
That  is,  they  may  be  operated 
either  with  or  without  the  float. 
Fig.  68  illustrates  the  type  of  a 
large  number  in  which  the  effort 
is  made  to  subdivide  the  liquid 
fuel  by  causing  eddies  or  spiral 
currents  in  the  air.  The  supply 
of  air  coming  in  from  the  bottom 
by  atmospheric  pressure  will  cause 
the  spindle  to  rise  which  carries 
the  vanes  or  propeller-shaped 
blades.  The  ascending  currents 
will  twist  the  spindle  and  give  a 
FIG.  68.  spiral  motion  to  the  air  in  the 

chamber  which  will  help  to  complete  the  mixing,  Sometimes 
these  helical  areas  are  doubled.  The  rise  of  the  needle-valve 
spindle  is  controlled  by  the  stop  at  the  top  of  the  mixer,  so  that 
the  supply  of  fuel  can  be  varied.  This  carbureter  could  work 
without  the  float-chamber  if  desired. 

114.  Carburetors  for  Motor-Vehicles.  Automatic  Car- 
buretors. —  While  all  of  the  modern  forms  of  float  and  floatless 
carburetors  have  been  applied  experimentally  to  motor- vehicles, 
the  recent  practice  of  builders  has  developed  some  principles 


CARBURATION  AND   CARBURETORS.  237 

of  design,  which  are  the  outcome  of  the  special  difficulties  as 
to  variable  fuel  supply  which  are  there  present. 

The  requirements  as  to  fuel  supply  in  these  motors  may  be 
summarized  as  follows: 

i.  The  adjustment  of  fuel  and  air  to  each  other  should  be 
as  automatic  as  possible,  under  all  varying  conditions.  The 
operator  of  the  motor  is  likely  to  .be  unskilled  in  making  this 
'adjustment  himself,  and  it  is  therefore  perhaps  not  desirable  that 
he  be  encouraged  to  alter  it.  But  the  mixture  is  a  combination 
of  the  liquid  fuel  (gasoline,  alcohol  or  kerosene)  with  the  gaseous 
air.  The  latter  will  be  subject  to  a  control  of  its  volume  while 
the  former  to  a  control  of  its  weight  in  a  given  time.  The  mass 
of  the  liquid  is  different  from  that  of  the  air,  by  reason  of  the 
great  density  difference  between  them.  Temperature  of  the  air 
will  have  great  effect  on  the  weight  occupying  a  given  bulk  or 
space,  and  the  hygrometric  state  of  the  air  affects  both  weight 
and  the  amount  of  oxygen  in  a  cubic  foot,  as  well  as  the  temper- 
ature of  the  resulting  mixture  after  ignition.  It  has  been  fre- 
quently noted  how  smoothly  and  "sweetly"  (to  use  a  colloquial- 
ism) the  motor  runs  in  the  evening  and  night,  as  compared  to 
the  day.  The  greater  density  without  inconvenient  lowering  of 
the  temperature  which  occurs  in  winter  is  doubtless  one  explana- 
tion of  this.  To  lessen  the  variation  of  air  quality,  the  modern 
method  is  to  draw  the  combustion  air  from  a  heated  zone,  such 
as  that  surrounding  the  exhaust  pipe  of  the  motor  by  means  of  a 
flaring  mouth-piece.  Or,  the  carburetor  may  be  heat-jacketed 
by  products  of  combustion,  or  hot- water- jacketed  from  the  out- 
flow of  warm  water  from  the  motor  jackets.  The  carburetor 
works  best  with  air  at  about  80°  F.  at  entry.  To  make  it 
warmer  is  to  diminish  the  oxygen  weight  inconveniently;  to  have 
it  cooler  is  to  retard  the  quick  ignition  of  the  fuel  and  air  mixture 
when  it  reaches  the  combustion  chamber.  To  keep  the  air  and 
fuel  at  constant  temperature  under  all  outside  temperature 
conditions  of  weather  is  to  secure  best  results  when  the  mixture 
is  once  correct. 


238  THE   GAS-ENGINE. 

2.  The  motor-car  presents  a  more  difficult  problem  in  service 
than  the  stationary  engine  under  uniform  load,  or  than  the 
motor-boat.  In  the  latter  the  variation  in  power  is  a  variation 
in  speed,  and  the  resistance  only  varies  outside  of  that  as  respects 
a  few  factors  which  do  not  vary  directly  as  the  speed.  Even  in 
buffeting  waves  and  against  a  head-wind  and  tide,  the  motor- 
speed  can  be  kept  up.  With  the  motor-car,  however,  the  follow- 
ing range  of  demand  must  be  met : 

(a)  A  minimum  speed  of  pistons  and  against  minimum  resist- 
ance, which  occurs  when  the  car  is  stopped  or  standing. 

(b)  A   minimum  speed  of    pistons    but    a    maximum    turn- 
ing resistance,  as  on   heavy  hills,  deep    and    heavy   road    sur- 
face, and    in  starting  or  working  amid   crowded   and  irregular 
traffic. 

(c)  A  maximum  piston  speed,  and  maximum  power  in    car 
speed  as  in  racing  or  in  speeding  with  full  loads  on  levels. 

(d)  Combinations  of  intermediate  piston  speeds  with  all   car 
speeds  and  intermediate  resistances,  as  in  hill  and  level  work  in 
open  country. 

(e)  The  requirement  of  minimum  fuel  waste  at  exhaust  in 
form  of  smoke,  and  of  maximum  efficiency  of  fuel  in  vehicles  of 
large  power  capacity  as  in  commercial  vehicles.     These  latter 
are  in  a  special  class  where  fuel  expense  is  significant,  and  which 
have  usually  a  time  schedule  to  maintain.     They  must  not  be 
stalled  on  the  road  because  at  any  time  the  excess  consumption 
as  emptied  the  fuel  tank. 

(/)  Changes  of  level  of  the  fuel  tank  relatively  to  the  carburetor 
or  the  changing  level  of  the  surface  of  the  liquid  fuel  in  the  tank 
must  not  vary  the  fuel  supply.  Grade  changes  must  not  also 
change  the  ratio  of  the  fuel  level  to  the  jet-nozzle  in  the  car- 
buretor itself.  The  jet  should  be  about  TV  of  an  inch  above  the 
fuel  level,  and  this  should  not  change  materially. 

(g)  The  varying  piston  speed  brings  with  it  a  variation  in  the 
compression  pressure  and  hence  in  the  mean  effective  pressure  of 
the  succeeding  expansion  stroke  when  the  water-cooling  system 


CARBURATION  AND  CARBURETORS. 


239 


is  effective.  The  compression  pressure  when  it  takes  place  at 
high  speed  is  nearly  adiabatic  (pars.  50,  203),  because  the  cooling 
water  in  the  jackets  or  the  direct  air-cooling  effect  has  scarcely 
time  to  lower  the  temperature  of  more  than  the  film  of  mixture 
which  is  nearest  to  the  cooling  surfaces.  At  low  speeds,  the 
mixture  is  exposed  longer  to  such  action  of  withdrawal  of  the 
heat  due  to  compression ;  the  heating  process  approaches,  there- 
fore, more  nearly  to  an  isothermal  (par.  49)  having,  therefore,  less 
energy  at  the  end  of  the  process,  and  giving  a  lower  mean  effective 
pressure  in  the  next  stroke.  This  is  the  same  in  effect  as  calling 
for  more  fuel  or  heat  energy  per  cubic  foot  of  cylinder  volume  at 
low  speeds  than  at  the  higher. 

(h)  The  high  piston  speed  with  a  given  area  of  exhaust  passage 
or  through  the  exhaust  valve,  keeps  more  heat  in  the  cylinder  by 
retarded  flow  of  the  products  of  the  combustion  of  the  last  stroke. 
The  hotter  cylinder  is  filled  with  a  less  weight  of  incoming  charge 
when  its  volume  is  filled,  as  compared  to  one  which  is  more 
effectively  cooled  by  the  longer  action  of  the  cooled  and  cooling 
walls.  This  is  the  same  as  a  throttling  effect  of  partial  closure 
of  the  controlling  or  accelerating  valve,  and  is  the  opposite  in 
effect  to  the  action  treated  in  the  previous  paragraph.  Every 
individual  motor  will  differ  from  all  its  alleged  duplicates  in  the 
sum  of  these  two  influences.  Constant-speed  motors  are  not 
subject  to  these. 

(i)  Constant-speed  motors  are  not  subject  to  the  variations 
of  effect  of  inertia  or  demand  for  acceleration  of  the  air  in  the 
inlet  passages.  The  elasticity  of  the  air  causes  it  to  expand  or 
compress  before  the  column  moves  as  a  whole  under  the  pressure 
of  the  external  atmosphere.  This  latter  is  the  force  which  sends 
the  air  into  the  carburetor  (there  is  no  such  thing  as  suction, 
regarded  as  a  force)  and  as  the  air  flow  induces  the  fuel  flow, 
variations  in  the  former  cause  corresponding  variations  in  the 
latter. 

Modern  carburetors  will  therefore  be  found  to  seek  after  these 
results : 


240 


THE  GAS-ENGINE. 


1.  Constant  temperature  and  moisture  conditions  for  the  air 
by  drawing  it  from  a  warmed  zone  close  to  hot  surfaces  about 
the  motor. 

2.  Constant  temperature  and   preheated   conditions   for  the 
fuel,  by  jacketing  the  fuel  chamber  of  the  carburetor,  and  using 
waste  heat  of  jackets  or  exhaust  to  secure  this.     (Fig.  258.) 

3.  Constant  level  adjustment  relative  to  the  fuel  jet  by  using 
an  annular  float  which  surrounds  the  jet  chamber  (as  in  Fig.  256) 
and  by  seeking  to  neutralize  inertia  effects  on  float  and  auto- 
matic fuel  valve,  by  counterbalancing  the  former  over  a  fulcrum 
by  a  weight   (Figs.  256  and  259)  on  the  valve-spindle,  or  by  a 


FIG.  254. 

spring  (Fig.  255).  The  spring  has  no  inertia  of  its  own  as 
respects  its  response  to  a  float  motion  due  to  a  jolt  or  jar,  and  its 
effect  can  be  varied  by  adjusting  its  initial  compression  by  a 
screw  and  nut. 

4.  But  the  feature  which  has  brought  automatic  action  nearer 
for  high-speed  work  has  been  the  introduction  of  the  automatic 
or  compensating  air  valve.  This  is  A  in  Fig.  254  and  D  in  Fig. 
255.  It  is  held  shut  when  the  air  column  is  moving  slowly 
towards  the  motor  outlet,  or  when  the  motor  is  at  rest.  In  hand- 
starting,  therefore,  the  flow  of  fuel  relatively  to  the  air  volume 
is  considerable,  and  the  mixture  rich  in  fuel,  making  the  first 
ignitions  easy  and  sure.  Fig.  254  shows  a  detail  at  V  whereby 


CARBURATION  AND   CARBURETORS. 


241 


the  depression  of  that  spindle  from  without,  forces  down  the 
annular  float  F,  raising  the  level  of  gasoline  around  the  jet,  and 
flooding  the  carburetor  with  excess  of  fuel.  As  the  motor  piston 
speeds  up,  the  aspiration  strokes  become  more  frequent  and 
the  tension  in  the  air  passage  grows  less,  increasing  the  flow  of 
fuel  through  the  jet  opening  due  to  the  atmospheric  or  other 
pressure  behind  it,  and  the  pressure  against  the  spring  which 
holds  the  automatic  shut.  The  spring  yields  more  and  more 
as  the  difference  of  pressure  increases  more  and  more  with  speed, 
opening  a  larger  and  larger  area  for  air,  until  the  maximum  is 
reached  at  the  highest  practical  speed.  While  the  fuel  flow 


FIG.  255. 


FIG.  256. 


increases,  therefore,  the  air  flow  increases  faster  by  reason  of  the 
increasing  area,  producing,  therefore,  a  mixture  relatively  leaner 
in  fuel  at  high  speeds,  while  the  fuel  flow  has  intrinsically  or 
actually  increased  with  the  speed.  Danger  of  pre-ignitions 
from  undue  compression  of  a  rich  mixture  is  prevented,  and  an 
excess  of  fuel  which  might  not  find  oxygen  enough  to  burn  in 
the  limited  time  of  the  high-speed  stroke.  The  high  speed 
favors  also  an  intimacy  of  mixture  of  the  fuel  and  air  due  to  the 
high  spraying  velocity  of  the  jet,  or  special  pains  in  design  may 
be  taken,  as  in  Fig.  256,  to  favor  mixing  by  the  shape  of  the 


242 


THE  GAS-ENGINE. 


nozzles  before  and  after  combination  has  occurred.     The  throttle 
acts  upon  the  completed  mixture  in  all  cases,  but  a  hand  adjust- 


ment  of  fuel  supply  to  the  jet  is  always  provided,  to  be  used  also 
as  a  shut-off  of  fuel  if  desired. 

*  The  author  is  indebted  to  the  courtesy  of  Mr.  Benj .  R.  Tillson  for  permis- 
sion to  use  Figs.  258  and  259  in  the  clear  form  here  presented. 


CARBURAT1ON  AND   CARBURETORS. 


243 


5.  Another  solution  looking  to  the  same  or  better  results  is 
to  place  two  carburetors  in  series,  or  tandem.  The  first  or 
smaller  one  is  for  running  the  engine  at  low  speeds  or  under 
lighter  demands  for  power.  It  has  its  own  throttle,  and  delivers 
into  the  intake  piping  between  the  motor  and  the  throttle  of  the 
second  or  larger  carburetor.  This  latter  has  the  automatic 
air- valve  provision,  fitted  with  a  dash-pot  detail  to  prevent  incon- 
venient fluctuations.  As  the  engine  will  be  speeded  up,  or  the 


To  Cylinders 


Throttle 


Spray  nozzle 


Auxiliary  air  valve 


•Auxiliary  air  valve  spring 


Adjustment  for  intermediate  speeds 


Adjustment  for  high  speeds 


Gasoline  pipe 
Gasoline  adjustment  for  low  speeds 


Dust  screen  over  air  inlet 


FIG.   259.* 


throttle  is  opened  wider,  with  increased  demand  for  power,  the 
second  carburetor  comes  into  play,  and  provides  a  full  capacity 
up  to  the  maximum  of  the  motor  with  that  fuel  and  with  a 
greater  fuel  efficiency.  A  copper  coil  of  pipe  brings  hot  exhaust 
gases  into  a  space  below  the  main  throttle  to  secure  constant 
temperature  and  necessary  heat  for  certain  vaporization.  The 
fuel  jet  plays  against  the  outside  surface  of  this  hot  coil  at  all 
times. 


244  THE  GAS-ENGINE. 

6.  To  secure  positive  and  increasing  flow  of  the  liquid  fuel 
to  the  carburetor  with  increasing  speed,  the  practice  of  putting 
the  fuel  tank  under  pressure  has  been  introduced.     This  pressure 
is  brought  from  the   exhaust  connections  by  a   by-pass  pipe  on 
top  of  the  liquid  in  the  tank,  and  being  a  gas  without  oxygen  it 
renders  the  tank  free  from  danger  of  an  ignition  of  an  explosive 
mixture  of  fuel  vapor  and  air.     By  increasing  the  difference  of 
pressure  on  the  two  sides  of  the  liquid  fuel,  the  flow  of  the  latter 
is  hastened  through  a  small  orifice,  which  is  thereby  more  quickly 
controlled;  by  using  exhaust  pressure,  the  fuel  pressure  is  greater 
as  the  speed  increases;  the  flow  is  not  made  variable  by  differences 
of  level  of  tank,  full  or  empty,  or  by  the  inclination  of  the  car- 
frame  on   grades  up   or  down.     Mountain-work   is  troublesome 
without  the  pressure  feed.     It  is  inconvenient  to  have  the  tank 
high  enough  to  secure  gravity  feed,  if  the  tank  is  large;  and  gravity 
feed  is  variable  with  the  amount  of  liquid  in  the  tank,  and  can 
never  be  equal  to  more  than  a  few  ounces  per  square  inch.     With 
the  pressure  feed,  however,  an  apparatus  to  get  up  pressure  is 
required  for  starting,  since  the  working  of  the  motor  is  required 
to  produce  the  pressure  feed  to  the  carburetor.     Or,  a  small  fuel 
tank  with  gravity  feed  may  be  used  to  start  the  carburetor  when 
the    motor   is   at   rest,   and   to   be   shut   off   when    pressure   is 
established. 

7.  Or  again,  instead  of  a  disk- valve  opening  by  air-pressure 
from  without,  a  flexible  diaphragm  may  be  used,  actuated  either 
by  differences  of  air  and  gas  pressure,  or  by  a  spring.     By  the 
motion  or  collapse  of  the  diaphragm  more  air  openings  are  made 
available,  and  an  increased  fuel  supply  may  be  effected  by  the 
same  motion.     Or  a  sleeve  or  thimble  with  holes  or  slots  may  be 
used,  whose  motion  under  spring  resistance  to  flow  may  open 
larger  areas  as  the  thimble  moves  in  front  of  openings  in  the 
casing  which  surrounds  it. 

In  motor-car  practice  to  date,  no  attempt  has  been  made  to 
supply  the  air  to  the  carburetor  under  pressure  by  mechanical 
means  such  as  a  fan  or  blower.  The  size,  weight,  and  speed  of 


C A RBU RATION  AND   CARBURETORS. 


245 


such  a  fan  would  make  an  inconvenient  addition  to  the  weight 
of  the  equipment,  and  the  power  to  operate  it  would  offset  the 
power  which  would  be  saved.  But  in  theory,  and  in  plants  of 
considerable  size,  the  serving  of  several  units  from  one  inde- 
pendently driven  pump,  particularly  if  motors  of  the  two-cycle 
type  were  to  be  operated,  would  offer  considerable  advantage  in 
securing  full  weight  of  charge  per  stroke,  and  could  relieve  the 
motor  of  the  function  of  supplying  mixture  of  fuel  and  air  for  the 
following  power  stroke. 

115.  Alcohol  Carburetors.  Martha,  Japy,  Richard,  Brouhot, 
Marienfelde. — The  only  difference  which  requires  to  be  made 
when  alcohol  is  to  be  used  as  the  fuel  and  it  is  to  be  atomized 
and  vaporized  in  a  carburetor  is  that  the  carburetor  must  be 


Gasolene 


FIG.  69. 


kept  hot  so  as  to  secure  the  vaporization  in  addition  to  the  simple 
atomizing  which  is  required  for  the  gasoline  carburetor  pre- 
viously discussed.  In  some  cases  the  conducted  heat  from  the 
working  cylinder  will  keep  the  pipe  hot  enough  to  vaporize  the 
alcohol  after  the  engine  is  once  working,  so  that  it  is  only  necessary 
to  get  the  engine  started  and  well  warmed.  After  this  the  same 
equipment  will  work  indifferently  on  alcohol  or  on  gasoline.  A 
convenient  plan  which  has  been  much  used  in  Germany  and  in 
France  is  to  make  the  carbureter  double,  as  is  shown  in  Fig.  69, 


246 


THE  GAS-ENGINE. 


which  illustrates  the  Marienfelde  design.  This  is  a  constant- 
level  or  float-feed  carburetor  into  which  air  enters  through  the 
orifice  at  the  left  hand  and  surrounds  the  two  jets  C  and  E  in 
an  annular  current.  The  gasoline  enters  at  the  right-hand 
chamber  and,  with  its  level  controlled  by  the  float  A ,  passes  into 
the  air-current  through  the  nozzle  at  C.  Above  the  jets  is  the 
shell  valve  B,  which  is  shown  in  the  position  in  the  cut  for  the  work- 
ing of  the  carburetor  with  alcohol  through  the  left-hand  inlet- 
float  D  and  jet  E.  The  engine  is  started  cold  with  the  gasoline 
side  in  action,  which  will  require  no  heat  in  the  connections  to 
start  the  motor.  After  the  motor  is  running  at  speed,  the  shell 
valve  is  turned  over  in  the  position  shown  in  the  cut,  when  the 
alcohol  begins  to  act  and  the  gasoline  supply  is  cut  off.  The 
valve  F  above  the  shell  valve  B  acts  as  a  throttle-valve  to  vary 
the  amount  of  air  and  fuel  which  passes  to  the  cylinder  from  the 
carbureter. 

The  more  usual  forms  do  not  use  the  double  principle,  but 
depend  upon  heating  the  atomized  alcohol  by  passing  it  in  a 
circuitous  passage  around  a  hot  exhaust-pipe.  In  the  Martha 
carburetor,  Fig.  70,  the  alcohol  enters  from  below  into  the  spray- 


Outlet  to  Engine 


wy  Spirit  Inlet 

FIG.  70. 

ing  part  of  the  carburetor  and  is  aspirated  by  the  charging  stroke 
with  the  air  which  enters  through  /.  The  alcohol  is  atomized 
by  contact  with  the  corrugated  surface  and  the  netting  in  the  part 
B,  from  which  it  enters  at  the  side  of  the  horizontal  chamber, 
which  is  the  vaporizer.  The  alcohol  vapor  and  air  move  in  the 
spiral  channel  in  contact  with  the  exhaust-conduit  and  thus  out 
to  the  engine. 


CARBU RATION  AND  CARBURETORS. 


247 


Pure  Air  Valve 


In  the  Brouhot  carburetor,  which  is  more  properly  called  a 
vaporizer,  the  exhaust-gas  enters  at  the  bottom,  as  shown  by  the 
inlet  arrow  (Fig.  71).  If  the  valve  which  regulates  the  mixture 
is  shut  tight,  the  exhaust-gas  passes  spirally  around  the  central 
tube  in  one  direction,  while  the  alcohol  passes  in  a  reverse 
spiral  in  the  other.  The  alcohol  spiral  ends  at  the  top  where 
the  vaporized  alcohol  meets  the  pure  air  and  they  pass  together 
to  the  motor.  The  exhaust-gases  descending  from  the  top 
passes  out  at  the  bottom  as  they  would  if  the  regulating- valve 
were  open.  Of  course  a  partial  opening  of  the  regulating-valve 
splits,  the  exhaust-current  so  that 
only  a  part  of  it  passes  through 
the  vaporizer. 

In  the  Richard  form  the  float 
principle  is  used  (Fig.  72),  and  the 
jacketing  of  the  impact  surface 
by  the  hot  products  of  combustion 
entering  at  e  and  leaving  at  e?  causes 
the  atomized  alcohol,  spread  in  a 
thin  film  on  the  hot  cone  by  the 
deflector  d,  to  become  a  gas  and  to 
move  to  the  engine  through  the 
outlet  m.  In  the  Japy  carburetor, 
illustrated  in  Fig.  73,  the  ribbing 
of  the  passage  L,  where  it  is  sur- 
rounded with  hot  gas,  makes  that 
surface  act  as  vaporizer  for  the 
alcohol  which  passes  through  the 
float-chamber  A  and  the  control- 


Alcohol 


ust  Gases 


FIG.  71. 


ling-valve  C.     The  inlet  of  air  at  E  is  controlled  by  the  valve  V. 

116.  Kerosene  Carburetors. — In  the  carburation  of  air  by 
kerosene  it  is  particularly  necessary  to  pay  close  attention  to 
the  vaporization  process.  In  the  discussion  of  the  kerosene-oil 
engine  in  its  earlier  forms  (par.  79)  the  difficulties  were  referred 
to  which  result  when  the  attempt  is  made  to  inject  the  liquid  oil 


248 


THE  GAS-ENGINE. 


without  atomizing.  The  motor  cylinder  either  becomes  coated 
with  a  hard  carbon  coat  resulting  from  decomposition  of  the 
oil  by  a  cracking  process,  or  the  cylinder  is  flooded  with  liquid 
oil  which  it  will  not  vaporize  completely.  If,  however,  the  .ato- 
mized mixture  of  carburated  air  is  drawn  through  a  vaporizer  at 
nearly  a  red  heat,  the  carbon  deposit  disappears,  apparently 
carried  away  by  the  next  succeeding  rush  of  air,  and  when  this 
carburated  hot  air  meets  the  main  supply  of  air  required  for 
combustion  and  is  thoroughly  mi&.xl  with  it,  the  combustion 
appears  to  be  practically  complete  without  deposit  of  carbon. 
Before  the  engine  starts,  the  vaporization  has  to  be  effected  by 
a  separate  source  of  heat  or,  as  discussed  in  the  paragraphs  above ; 
or  the  engine  may  be  started  on  a  more  volatile  liquid,  such  as 
gasoline,  and  be  changed  over  to  kerosene  when  the  motor  has 


FIG.  72. 


FIG.  73. 


become  well  heated.  It  will  be  apparent,  however,  that  where 
the  heat  from  the  exhaust-gases  is  used  as  a  supply  to  meet  the 
vaporizer,  the  regularity  of  its  action  must  be  affected  by  every 
condition  which  varies  the  discharge  of  heat  in  the  exhaust,  so 


CARBURATION  AND  CARBURETORS.  249 

that  every  stroke  without  explosion,  every  slow-down  with  dimin- 
ished fuel  energy  in  the  charge,  and  every  stop  of  the  motor 
permitting  a  cooling  of  the  vaporizer,  will  interfere  with  its  regu- 
larity. Reference  should  be  made  to  paragraphs  32  and  83. 

117.  Some  Principles  of  Design  of  Carburetors. — In  the 
design  of  gasoline  carburetors,  experiment  seems  to  show  that 
a  good  spraying  effect  at  the  jet  is  best  secured  by  a  velocity  of 
the  incoming  air  past  the  nozzle  between  75  and  80  feet  per 
second.  Some  experiments  made  by  Mr.  L.  Berger  have  indi- 
cated that  when  the  suction-pipe  between  the  carburetor  and  the 
motor  is  sufficiently  hot  to  cause  the  globules  of  liquid  gasoline 
to  form  a  gas  on  striking  the  hot  surface,  35  square  inches  of 
surface  per  horse-power  at  a  temperature  of  180°  F.  will  secure 
complete  vaporization  at  atmospheric  pressure.  The  vapor  of 
gasoline,  according  to  these  same  experiments,  diffuses  in  the  air 
with  a  velocity  of  0.2  of  an  inch  per  second.  So  that  if  the  velocity 
of  flow  of  the  incoming  charge  is  known,  the  length  of  the  suction 
pipe  can  be  calculated  so  that  the  gasoline  vapor  may  have  time 
to  permeate  completely  the  air  by  coming  laterally  from  the 
walls  of  the  pipe  before  the  mixture  is  admitted  to  the  cylinder. 

With  kerosene,  on  the  other  hand,  about  31  square  inches 
of  vaporization  surface  are  required  per  horse-power,  heated  to 
a  temperature  of  390°  F.  at  atmospheric  pressure.  When  this 
principle  is  carried  out  in  a  kerosene  motor  the  volume  between 
the  atomizer  and  the  suction-valve  of  the  motor  will  become 
nearly  equal  to  the .  volume  of  the  piston  displacement  with  a 
high-speed  motor. 


CHAPTER  XL 

IGNITION. 

120.  Introductory. — It  has  been  already  considered  that  the 
problem  of  increasing  the  heat  energy  of  the  mixture  of  gas  and 
air  behind  the  working  piston  demanded  that  after  the  mixture 
had  been  compressed  it  should  be  ignited  so  that  the  gas  should 
burn  in  the  oxygen  of  the  mixture  and  impart  the  increased 
pressure  due  to  this  heat.     This  ignition  should  be  so  timed  as 
to  occur  at  the  proper  point  of  the  cycle  so  far  as  the  gas  is  con- 
cerned and  at  the  proper  point  of  the  stroke  of  the  piston  so  far 
as  the  motor  is  concerned.     In  the  Otto  cycle  this  ignition  is  to 
take  place  at  such  a  point  that  the  combustion  shall  be  complete 
or  nearly  so  when  expansion  begins.     There  have  been  many 
methods  proposed  for  the  accomplishment  of  this  purpose,  each 
of  which  offers  certain  features. 

121.  Ignition  by  an  Auxiliary  Flame. — The  plan  of  igniting 
the  mixture  by  an  auxiliary  flame  was  early  tried.     In  its  simplest 
form  it  consisted  of  having  two  jets  or  burners  connected  to  the 
gas-supply  by  flexible  tubes.     These  jets  were  alternately  pre- 
sented to  the  explosive  mixture  and  ignited  it.     The  ignition  of 
the  explosive  mixture  was  necessarily  followed  by  the  extinction 
of  the  auxiliary  jet,  so  that  this  required  a  secondary  or  free  jet 
burning  in  the  open  air  by  which  the  igniting  jet  could  be  lighted 
after  each  succeeding  extinction.     One  of  the  earliest  forms  of 
this  combination  of  igniting  jet  and  continuous  lighting  jet  was 
the  system  of   Barnet,  whereby  the    igniting  jet  burned  within 

a  shell  or  casing  which  rotated  like  a  valve,  presenting  the  open- 

250 


IGNITION.  251 

ing  in  the  casing  alternately  to  the  explosive  mixture  in  the 
cylinder  and  the  lighting  jet  which  burned  outside  of  it.  This 
system  is  open  to  the  very  serious  objection  of  the  escape  of  gas 
with  its  attendant  odor,  and  it  is  not  available  for  use  in  the  open 
air.  If,  at  any  time,  both  flames  were  extinguished,  the  engine 
ceased  to  operate.  It  could  also  give  only  about  40  ignitions  per 
minute.  Very  ingenious  combinations  of  the  flame-ignition,  and 
the  slide-valve  have  been  made  in  the  design  of  Otto  engines, 
with  a  view  to  increasing  the  number  of  ignitions  to  over  100 
per  minute  and  to  secure  continuity  of  the  igniting  flame  and 
overcome  the  flow  of  the  flame  in  the  wrong  direction  when  the 
pressure  due  to  the  compression  was  greater  than  the  pressure 
which  the  jet  would  resist. 

122.  Ignition  by  Internal  Flame. — In  the  Brayton  cycle  the 
igniting  flame  was  kept  burning  continuously  within  the  working 
cylinder  itself.     This  arrangement  was  possible  with  the   con- 
tinuous heating  process  of  the  Brayton  cycle  as  long  as  the  supply 
of  mixture  flowed  through  the  open  valve.     Since  the  pressure 
in  the  working  cylinder  was  enough  greater  than  that  in  the 
reservoir  which   supplied   the   continuous   burner,    there   was   a 
tendency  for  the  flame  to  be  blown  out  by  a  reversal  of  the  direc- 
tion   of   flow  in    the    jet.     A  safeguard  had  to  be  abundantly 
provided,   lest   the  flame   should   blow  back  into   the   reservoir 
within  which  it  would,  of  course,  be  propagated  and  would  result 
in  an  explosion.     This  was  secured  by  a  provision  of  wire-gauze 
safety  attachment,  but  in  case  of  the  deterioration  of  this  gauze 
the  danger  was  always  present.     This  gauze  was  an  element  of 
weakness  in  the  Brayton  engine,  and  in  spite  of  care  the  flame 
would  become  occasionally  extinguished,   when,   of  course,   the 
operation  of  the  engine  stopped. 

123.  Ignition  by  Heated  Metal  from  External  Jet. — A  system 
of  ignition  which  avoided  bringing  a  flame  or  jet  into  the  cylinder 
was  to  ignite  the  mixture  by  bringing  into  it  by  the  action  of  a 
slide-valve,  a  surface  which  had  been  heated  outside  the  cylinder 
by  the  action  of  an  auxiliary  jet  or  flame  in  which  the  surface 


252  THE  GAS-ENGINE. 

stood  at  rest  during  the  phases  of  the  cycle  in  which  there  was 
no  necessity  for  ignition.  The  difficulty  connected  with  this 
system  was  the  uncertainty  that  the  metal  surface  could  be  heated 
sufficiently  to  insure  ignition  when  the  mixture  was  such  as  to 
ignite  reluctantly  by  reason  of  its  impoverishment,  and  the  diffi- 
culty connected  with  the  deterioration  of  metal  exposed  to  oxida- 
tion at  high  heat.  This  metal  igniter  was  often  made  in  cage 
form,  so  that  a  large  metal  surface  should  be  exposed  to  the  gas 
as  soon  as  it  was  intruded  into  the  combustion-chamber. 
(Clerk.) 

124.  Ignition  by  Catalysis  — It  has  long  been  known  that  one 
of  the  properties  of  spongy  platinum  (known  as  catalysis)  is  that 
the  impact  upon  it  of  a  jet  of  combustible  gas  would  so  raise  its 
temperature  that  it  would  act  as  an  igniter.     This  property  was 
thought  of  and  applied  to  a  limited  extent  for  gas-engines,  but 
had  the  objection  that  with  a  mixture  of  varying  richness  the 
ignition  was  not  positive  nor  reliable. 

125.  Ignition    by    Incandescent   Wire    or   Cage    Electrically 
Heated. — In  order  to  avoid  the  objections  connected  with  the 
flame-heating  of  a  metal  to  be  introduced  into  the  combustion- 
chamber,  the  plan  has  been  used  of  heating  a  coil  of  platinum  or 
other  lesistant  wire  or  thin  strips  of  platinum  by  means  of  the 
resistance  which  they  offer  to  the  passage  of  an  electric  current. 
This  incandescent  platinum  is  carried  on  a  slide  from  which  it 
is    electrically  insulated    and  is  introduced   white-hot  into   the 
explosive  mixture.     By  this  plan  any  danger  of  blowing  out  of 
flame  is  avoided,  the  temperature  of  the  incandescent  metal  can 
be  made  high  enough  to  insure  ignition,  and  several  of  the  ob- 
jections to  the  previous  systems  are  avoided.     The  objections 
to  the  plan  are  those  incident  to  the  presence  and  unreliability 
of  the   electrical   apparatus   to   produce  the   incandescence.     If 
electrical  methods  are  to  be  used,  the  sparking  plan  presently  to 
be  discussed  is  more  convenient  and  cheap. 

126.  Ignition  by  Hot  Tube. — A  plan  of  ignition  which  offers 
some  advantages  is  to  pass  the  gas  mixture  into  a  tube  of  platinum, 


IGNITION. 


253 


porcelain,  nickel-steel,  or  similar  fire- resisting  material,  which  is 
kept  incandescent  by  an  external  flame  (Fig.  76).  The  entry 
of  a  small  portion  of  the  mixture  into  this  tube  brings  it  to  the 
ignition-point,  and  the  fire  is  propagated  through  the  entire  mass 
from  this  one  point.  The  objection  to  this  system  is  the  fragility 
of  the  incandescent  tube  if  made  of  porcelain,  which  is  liable 
to  break  under  jars  or  as  the  result  of  accidental  injury.  When 
platinum  or  steel  is  used  the  tube  is  not  so  fragile,  but  the  system 


FIG.  76. 

is  more  costly  and  the  tube  oxidizes  or  deteriorates.  With  the 
gasoline  motors  a  special  burner  for  burning  the  gasoline  is  re- 
quired which  shall  keep  the  tube  hot. 

In  the  handling  of  this  system  of  igniting  many  designers 
have  used  a  timing-valve,  which  should  open  the  hot  tube  to 
the  explosive  mixture  compressed  in  the  cylinder  just  at  the  right 
moment  to  have  the  ignition  propagate  itself  from  the  tube  to  the 
full  volume  of  mixture.  The  American  designers  have  not  used 
the  timing-valve,  finding  that  by  adjusting  the  flame  which  heats 


254  THE   GAS-ENGINE. 

the  tube  to  different  points  in  its  length  it  is  possible  to  vary  the 
time  at  which  with  varying  compressions  and  characters  of  mix- 
ture the  full  ignition  shall  occur.  The  time  of  ignition  with  the 
hot  tube  will  depend  upon: 

1.  The  length  of  the  tube. 

2.  The  size  or  volume  of  the  passage  leading  to  the  tube. 

3.  The  amount  or  degree  of  compression  of  the  mixture  by 
the  piston. 

4.  The  temperature  of  the  tube;    the  hotter  the  tube,  the 
earlier  the  ignition;  the  cooler  the  tube,  the  later. 

5.  The   fact  whether   it  was  hottest  near  the  open  or  the 
closed  end ;  if  heated  near  the  open  end,  the  earlier  the  ignition. 

6.  The  temperature  of  the  mixing-  and  ignition-chambers. 

7.  The  temperature  of  the  jacket-water  outlet. 

8.  The  speed  of  the  engine. 

9.  The  quality  or  proportions  of  the  air  and  fuel  admitted. 

10.  The  pressure  of  the  intake  or  suction  stroke. 

11.  The  governing  action  and  the  system  of  governing. 

12.  Leakages:   at  piston,  at  exhaust,  past  valves. 

13.  The  state  of  the  surfaces  of  the  tube,  outside  and  in. 

14.  The  location  of  the  tube,  with  respect  to  receiving  and 
acting  on  new  or  fresh  mixtures,  or  mixtures  containing  burnt 
gases. 

It  will  be  apparent,  therefore,  that  where  an  engine  is  to  run 
at  variable  speeds  and  powers  so  that  the  governing  process  is 
to  vary  Nos.  8,  9,  10,  and  n  from  stroke  to  stroke,  and  particu- 
larly in  automobile  practice,  where  it  may  be  desirable  to  retard 
the  ignition  sometimes  until  after  the  piston  stroke  has  begun 
and  been  partly  made,  the  hot  tube  has  given  way  before  the 
electric  ignition  methods.  The  hot- tube  ignition  cannot  be 
retarded  without  a  timing- valve,  and  even  with  it  it  is  uncertain. 
A  nickel-steel  tube  about  4  inches  long  of  J"  thickness  of  walls 
and  with  a  j\"  hole  through  it  will  last  about  three  years  when 
heated  continuously  to  a  good  red  heat. 


IGNITION.  255 

127.  Ignition    by    High    Temperature    of    Compression. — In 

the  Hornsby  and  in  the  Diesel  oil-engines,  ignition  is  secured  by 
the  expedient  of  having  the  compression  space  of  the  cylinder 
kept  hot  by  having  no  water-jacket  at  this  point  of  the  cylinder, 
so  that  when  the  piston  returns  and  compresses  the  air  behind  it 
the  temperature  of  that  air  shall  be  so  raised  by  compression  that 
a  jet  of  combustible  oil  entering  that  air  will  be  at  once  raised 
above  the  firing-point  and  will  ignite  without  flame  or  spark. 
This  system  requires  that  in  order  to  start  the  engine  the  com- 
bustion-chamber shall  be  heated  from  without  by  some  form 
of  lamp  or  heater  until  it  is  hot  enough  to  produce  the  first  ignition^ 
After  that  it  will  be  kept  at  ignition  temperature  as  long  as  the 
engine  is  working,  provided  the  governing  action  does  not  so 
impoverish  the  mixture  that  it  will  not  ignite  within  the  com- 
pression limits  at  which  the  engine  is  working.  These  engines, 
therefore,  must  always  receive  a  charge  of  combustible  so  that  there 
may  be  a  source  of  heat  to  keep  up  the  temperature  even  when 
the  engine  is  lightly  loaded.  If  the  weight  of  fuel  is  so  reduced 
by  governing  under  light  or  variable  loads  as  to  furnish  too  little 
heat,  the  strokes  will  gradually  become  less  powerful  as  the  com- 
pression-chamber cools,  until  finally  the  engine  stops. 

With  heavy  loads  and  high  compressions,  where  any  fuel 
may  have  remained  unburned  from  a  previous  charge,  this  system 
gives  trouble  from  back-firing  or  pre-ignitions.  Pre-ignitions  of 
this  character  often  result  from  the  presence  in  the  combustion- 
chamber  of  any  projection  or  small  isolated  mass  from  which  the 
conduction  of  heat  will  be  slow,  so  that  from  the  compressions 
and  ignitions  this  projecting  part  may  become  highly  heated, 
and  heated  faster  than  it  can  be  cooled  by  conduction.  Such  a 
projection  will  ignite  the  compressed  mixture,  even  while  the 
general  surface  of  the  cylinder  and  combustion-chamber  may 
be  too  effectively  cooled  to  do  so.  A  piece  of  an  asbestos  gasket 
sticking  out  of  its  joint;  or  a  bolt-head;  or  the  heated  points  of 
the  terminals  of  an  intended  electric  system,  will  act  in  this  way. 
Even  in  a  water-jacketed  cylinder  with  unusually  heavy  loads  the 


256 


THE   G4S-ENG1NE. 


cylinder  metal  may  itself  become  hot  enough  to  ignite  the  charges 
for  a  while,  even  when  the  regular  ignition  system  is  out  of  action. 
The  air-cooled  motor  will  often  prove  reluctant  to  stop  from  this 
same  action.  The  objection  to  the  system  is  its  uncertainty  with 
low  and  variable  compressions  and  widely  varying  loads.  Its 
advantage  is  its  avoidance  of  all  subsidiary  apparatus  to  cause  the 
desired  ignition,  and  its  dependence  upon  a  fundamental  law. 

128.  Ignition  by  Electrodes  and  Electric  Spark.  The  Jump- 
spark  System. — The  exceeding  convenience  and  compactness 
of  an  electric  system  of  ignition  of  the  explosive  mixture  in  a  gas- 
engine  cylinder  early  directed  attention  to  this  method.  It  was 


used  by  Lenoir  in  his  historic  motor.  The  principle  is  to  cause 
a  spark  of  sufficient  intensity  to  pass  between  two  terminals  on 
an  electric  circuit,  the  spark  to  be  in  the  mixture  which  its  heat 
is  to  ignite  (Fig.  77).  It  is  only  necessary,  therefore,  to  insert 
into  the  compression  volume  behind  the  piston,  a  plug  P  insulated 
from  the  metal  of  the  cylinder  walls  and  carrying  into  the  cylinder 
and  its  mixture  the  two  points  c,  c,  of  some  resisting  metal  with 
a  spark-gap  between  them,  and  then  at  the  proper  instant,  as 
determined  by  k  on  the  shaft  S  of  the  motor,  to  make  the  electric 
current  jump  the  gap  and  fire  the  mixture.  Fig.  78  shows  the 


IGNITION. 


257 


general  appearance  of  the  plug  with  the  cylinder  terminals  pro- 
jecting at  the  bottom.  The  plug  usually  fits  a  standard  half -inch 
pipe-thread,  and  may  easily  be  inserted  or  renewed.  The  inner 
point  in  the  form  illustrated  is  insulated  electrically  by  a  porce- 
lain or  mica  or  lava  or  soapstone  lining  or  core  from  the  metal 
of  the  engine,  while  the  outer  terminal  is  in  electrical  or  metallic 
contact  with  the  engine  or  its  frame  or 
mounting.  The  spark  therefore  passes 
the  gap  in  contact  with  the  mixture  when 
the  exterior  circuit  is  excited.  The  failing 
cases  for  these  plugs  are  the  closing  of  the 
gap  by  oil  or  lampblack  deposit  or  by 
water,  so  that  the  spark  does  not  form,  be- 
cause there  is  no  gap  for  it  to  jump;  or  the 
breakage  of  the  insulating  material  where- 
by the  current  is  short-circuited  in  the 
plug  and  does  not  reach  the  points.  If 
the  gap  is  filled  up,  it  can  be  formed  anew 
by  washing  the  points  in  liquid  gasoline; 
if  the  gap  has  become  too  wide  by  the  erosion  of  the  points  by 
heat,  the  spark  will  not  jump  across,  and  they  should  be  brought 
together.  About  a  sixteenth  of  an  inch  is  the  working  distance 
with  ordinary  electrical  currents  used  in  motors.  Fig.  78  also 
shows  the  double-gap  arrangement  which  has  been  found  to 
contribute  to  the  certainty  of  the  passage  of  the  spark.  The 
sec  nd  gap  is  external  to  the  cylinder  and  does  not  become 
fouled;  it  shows  plainly  to  the  eye  whether  the  spark  is  passing, 
its  resistance  acts  to  intensify  the  igniting  spark. 

There  are  two  systems  or  principles  of  electric  ignition.  One 
is  called  the  jump-spark  system,  and  depends  upon  the  principle 
which  is  utilized  in  the  Ruhmkorff  or  Faradaic  coil,  whereby  a 
secondary  current  of  high  intensity  flows  through  a  coil  of  fine 
wire  which  surrounds  a  primary  coil  of  coarser  wire  when  the 
primary  current  is  made  or  broken,  so  that  the  flow  of  electrical 
energy  is  intermittent  in  that  primary  circuit.  In  Fig.  79,  for 


FIG.  78. 


258 


THE  GAS-ENGINE. 


example,  which  shows  a  typical  arrangement,  the  primary  circuit 
starts  from  the  primary  or  storage  battery  at  the  left,  and  its 
wires  A  and  R  are  shown  in  heavy  lines.  The  motor  is  at  the 
lower  centre,  and  the  primary  circuit  is  made  and  broken  by  the 
contact  end  K  on  the  spring  L,  which  bears  against  a  commutator 
surface  en  the  motor  shaft.  This  surface  carries  a  conducting 
arc  H,  so  that  as  the  shaft  revolves  the  primary  circuit  will  be 
made  when  H  passes  under  K  and  L.  This  primary  circuit 
ends  in  a  few  turns  of  large  wire  (perhaps  No.  14)  around  the 


FIG.  79. 

core  of  the  coil  above.  Outside  of  this  is  the  secondary  coil 
(perhaps  of  No.  36  wire)  making  a  large  number  of  turns  and 
shown  in  Fig.  79  by  the  finer  lines.  This  secondary  circuit  has 
the  sparking-plug  T  in  it,  projecting  into  the  motor  cylinder. 
When,  therefore,  the  main  switch  on  the  primary  circuit  is  closed 
(it  is  shown  open  at  the  lower  left  hand  of  Fig  79),  and  the  motor 
revolves,  the  primary  circuit  will  be  closed  at  an  adjusted  angle 
of  the  motor-crank,  whereupon  a  stream  of  sparks  of  high  in- 


IGNITION. 


259 


tensity  will  cross  the  gap  at  the  plug  and  fire  the  charge.  In 
the  arrangement  shown  in  Fig.  79,  the  vibrator  or  trembler  B  is 
made  to  vibrate  very  rapidly  by  the  make-and-break  of  primary 
circuit  which  occurs  at  B,  so  that  while  H  and  K  are  in  contact 
mechanically  several  electric  makes-and-breaks  occur  at  the  coiL 
The  other  way  to  effect  this  same  flow  is  the  mechanical  vibrator 
shown  in  Fig.  80.  Here  the  shaft  of  the  motor  C  is  recessed,  so 


FIG.  80. 

that  the  vibrator  T  is  held  away  from  the  contact-point  K  except 
when  the  end  of  T  falls  into  the  recess.  The  primary  circuit 
is  then  made  through  T  and  K  to  the  primary  terminals  M  and 
P  and  causes  the  secondary  to  flow  through  B  to  the  spark-plug. 
By  giving  a  certain  mass  to  the  contact  end  of  T  the  latter  will 
vibrate  against  and  away  from  K,  while  the  shaft-gap  is  passing, 
making  and  breaking  the  primary  circuit  mechanically,  which 
is  followed,  of  course,  by  similar  breaks  in  the  secondary,  and  a 
flow  of  sparks. 

It  will  be  apparent  from  either  of  the  two  preceding  illustra- 
tions or  from  Fig.  81  that  this  system  of  making  contact  by  a 
commutator  surface  on  the  motor  shaft  and  a  conducting  arc  B 
makes  it  very  easy  to  advance  or  retard  the  moment  of  the  passage 
of  the  igniting-spark  relatively  to  the  dead-centre  of  the  piston 
stroke.  By  arranging  that  the  centre  of  the  vibrator  H  in  Fig.  81 
may  have  an  adjustment  angularly  around  A  by  hand  or  by 


260 


THE  GAS-ENGINE. 


governor,  the  angular  position  of  the  sparking  instant  is  obviously 
varied.  The  limit  to  this  adjustment  which  is  wise  may  easily 
be  set  by  stops  which  shall  prevent  too  wide  a  range  of  variation 
of  the  ignition.  Too  early  ignition  may  cause  the  engine  to  start 
backward;  too  late  ignition  may  cause  the  flaming  of  the  mix- 
ture to  be  still  in  progress  when  the  exhaust  opens. 

The  advantages  of  the  jump-spark  system  are  the  "avoiding 
of  any  moving  parts  inside  the  cylinder,  and  the  strong  spark 


FIG.  81. 

which  results  even  from  low  battery  power  in  the  primary  circuit, 
A  battery  of  four,  six,  or  eight  cells,  giving  a  voltage  of  from  4! 
to  6  volts  with  f  or  i  volt  per  cell,  and  an  amperage  of  8  to  16 
amperes  is  about  the  usual  standard.  Storage  batteries  giving  a 
capacity  of  from  100  to  300  ampere-hours  are  much  in  use  for 
automobile  motors-  Dry  batteries  with  carbon  and  zinc  ele- 
ments and  depending  on  the  usual  sal-ammoniac  paste  are  apt 
to  grow  weak  as  the  paste  dries  with  time. 

129.  Ignition  by  Electric  Arc.  Hammer-break  System. — 
The  other  system  of  electric  ignition  does  not  use  the  secondary 
circuit,  but  depends  upon  the  fact  that  a  break  in  th ;  flow  of  a 
primary  electric  current  will  reveal  an  arc  or  spark  passing  between 
the  broken  ends,  until  the  distance  between  them  becomes  too 
great  for  the  arc  to  jump.  If  such  a  break  can  be  made  inside 
the  cylinder,  and  so  that  the  arc  when  formed  is  surrounded  by 
the  explosive  mixture,  its  heat  will  ignite  it  and  the  stroke  will 


IGNITION. 


261 


be  made.  Fig.  82  shows  a  typical  arrangement.  The  cam  at 
the  bottom  is  so  timed  that  it  shall  lift  the  toe  D  outside  the 
cylinder  and  carry  inside  the  angular  motion  which  D  trans- 
mits to  C  at  the  proper  instant.  The  angular  motion  of  D 
and  C  causes  the  arm  or  lever  inside  the  cylinder  to  be  torn 
away  from  the  contact  surface  of  the  insulated  pillar  against 
which  it  rests.  The  severing  of  this  contact  causes  the  arc  to 
pass  and  fires  the  charge.  The  spring  E  causes  the  contact  to  be 
remade  when  the  push-rod  G  is  forced  away  from  D  by  the  pin  Z, 
and  the  inclined  surface  K.  From  the  fact  that 
^  the  contact  terminals  must  waste  away  by  the  elec- 
tric oxidation  caused  by  the  passage  of  the  spark, 
it  is  usual  to  give  some  enlargement  to  the  contact 
end  of  the  internal  lever,  so  that  it  receives  some- 
thing the  shape  of  a  hammer  on  a  handle.  This 
has  caused  this  arc  method  to  be  often  known  as 
the  hammer-break  system.  It  is  also  called  the 
contact  system.  To  give  greater  intensity  and 
duration  to  the  arc  a  sparking-coil  is  usually  in- 
serted in  the  circuit,  consisting  of  a  coil  of  about 
No.  14  insulated  wire  surrounding  a  core  made 
of  a  bundle  of  soft  Swedish-iron  wires  of  No.  20 
gauge  and  from  6  to  8  inches  long.  Such  a 
coil  acts  as  a  sort  of  condenser,  and  increases  the 
tendency  of  the  current  to  flow  across  the  gap  after 
the  break  is  made.  If  its  resistance  is  excessive  it  takes  too 
much  battery  power  and  current,  which  will  deteriorate  the  con- 
tacts unnecessarily.  From  ij  to  2  amperes  is  usually  enough 
battery  capacity. 

The  failure  of  this  system  comes  about  either  from  the  inter- 
position of  non- conductive  deposit  on  the  terminals,  so  that  no 
current  passes,  or  from  a  conductive  deposit  which  short-circuits 
the  current  and  prevents  the  arc,  so  that  there  is  no  arc  formed 
across  a  gap.  Deposits  have  been  mitigated  in  ill  effect  by  making 
the  contact  of  the  terminals  a  wiping  or  sliding  one,  so  that  the 


FIG.  82. 


262  THE  GAS-ENGINE. 

abrasion  of  the  moving  element  kept  the  fixed  one  clean.  It  is 
also  an  objection  to  the  system  that  it  compels  moving  parts  to 
be  inserted  into  the  hot  combustion- chamber  and  to  pass  through 
stuffing-boxes  in  the  walls  of  that  chamber.  To  give  a  spark  of 
a  given  intensity,  this  system  requires  more  battery  power  than 
the  other.  On  the  other  hand,  there  are  fewer  points  where 
failure  of  the  system  may  lurk,  since  there  is  but  one  circuit  and 
not  two,  and  no  vibrator  or  trembler  is  required. 

130.  Dynamo-  or  Magneto-electrical  Ignition.  General. — 
In  the  foregoing  discussion  the  source  of  electrical  energy  has 
been  some  form  of  battery.  It  is  obvious  that  an  electrical  cur- 
rent can  be  generated  by  the  revolving  armature  of  a  dynamo 
or  magneto-electrical  machine,  from  whose  action  the  necessary 
spark  action  can  be  secured,  and  the  cost  and  deterioration  in- 
cident to  battery  action  can  be  avoided.  Hence  a  tendency  to 
use  generators  is  a  feature  of  many  modern  designs,  partic- 
ularlly  of  automobile  motors.  The  dynamo  can  be  quite  small 
and  light  in  weight,  having  its  armature  driven  at  from  i~x>  to 
2000  revolutions  per  minute  by  belt  or  friction  drive  from  the 
motor- shaft,  and  giving  a  current  of  10  volts.  The  objection 
is  obviously  that  a  battery  either  of  primary  or  storage  type  is 
required  to  start  the  motor  from  rest.  The  storage  battery  is 
more  usual,  since  the  dynamo  can  be  wired  to  charge  it  while 
the  motor  is  running.  Such  dynamo  and  battery  can  also  be 
used  for  lighting  the  lamps  for  night  use.  The  power  consumed 
is  small,  and  its  cost  is  offset  by  the  convenience  of  having  fewer 
battery  cells. 

The  general  argument  concerning  electrical  ignition  in 
either  form  urges  against  the  system  the  troubles  from  defective 
wiring,  chafing  of  the  wires  in  moving  motors,  short  circuits 
from  water,  and  leakage  of  current  from  poor  insulation.  The 
deterioration  of  the  batteries,  and  the  defective  contacts  from 
dirt,  oxidation,  loosened  connections,  and  the  like,  can  be  avoided 
by  careful  attention  and  inspection.  The  electric  systems  also 
fail  when  the  quality  of  the  mixture  to  be  ignited  or  its  tempera- 


IGNITION.  263 

hire  falls  off,  so  that  a  "fat"  spark  of  normal  intensity  will  not 
insure  a  satisfactory  ignition.  In  old  weather  and  with  a  cold 
motor  it  will  easily  happen  that  ignition  will  fail  at  the  start. 
With  battery  circuits  this  can  be  avoided  by  using  more  calls 
in  starting  than  will  be  required  after  the  motor  is  warmed  to 
its  work,  and  gradually  cutting  cells  out  of  the  circuit  until  only 
those  are  in  use  which  are  needed.  The  spark  must  plainly  be 
powerful  enough  to  raise  the  mixture  at  the  igniting-point  to  the 
necessary  temperature  for  a  propagation  of  the  flame.  This 
temperature  will  be  higher  for  a  lean  than  for  a  rich  mixture,  and 
variation  of  quality  may  make  variation  of  the  spark  intensity 
necessary  if  governing  of  the  motor  acts  to  impoverish  the  working 
mixture. 

It  will  be  apparent,  of  course,  that  a  failure  of  the  ignition 
system  must  cause  the  motor  to  stop,  and  an  opening  of  the 
switch  on  an  electric  ignition  circuit  is  an  effective  means  of  stop- 
ping the  motor  for  short  periods  in  automobile  practice. 


CHAPTER  XII. 

GOVERNING. 

135.  Introductory.—  The  gas-engine  differs  from  the  steam- 
engine  in  the  method  to  be  used  to  vary  the  effort  as  the  resistance 
varies,  by  reason  of  the  fact  that  it  does  not  draw  a  supply  of 
energy  from  a  reservoir,  but  that  the  energy  is  generated  by  com- 
bustion in  the  cylinder  for  each  working  stroke.  The  capacity  of 
the  governor  to  increase  the  power  of  the  cylinder  at  need  is 
much  more  limited  than  in  the  steam-engine. 

It  follows,  therefore,  that  the  methods  which  are  usual  for 
the  steam-engine  require  not  only  modification  but  recon- 
struction when  applied  to  the  problem  of  governing  speed  under 
variations  of  load.  The  same  principles  which  apply  in  the 
steam-engine  apply  to  the  gas-engine,  concerning  the  desirability 
o.  making  t"  e  speed  of  the  engine  as  nearly  automatically  con- 
trolled by  the  governor  action  as  is  possible,  and  that  the  governor 
should  be  isochronous,  in  the  sense  that  it  shall  make  the  engine 
perform  its  cycle  in  equal  times  under  all  variations  of  load. 
Referring  back  to  the  fundamental  formula, 


33,000 
it  will  be  apparent  that  this  can  be  written 


after  the  engine  has  been  actually  constructed,  since  A  and  L  are 
not  variables  and  33,000  is  a  constant  factor,  so  that  the  fraction 

264 


AL 

can  be  denoted  by  K.    If  it  be  desirable    to  keep  the 

33,000 

number  of  revolutions  invariable  as  the  horse-power  varies,  the 
quantity  to  be  varied  will  be  the  pressure  P,  and  the  methods 
to  be  used  will  be  directed  to  produce  that  variation.  But  the 
engine  will  be  at  its  best  when  working  with  the  maximum  value 
for  P  for  its  normal  condition;  hence  the  governor  as  a  rule  acts 
mainly  to  diminish  P  as  the  resistance  diminishes.  The  gov- 
ernor will  usually  be  of  the  shaft  type  with  revolving  weights 
which  are  moved  outward  by  the  acceleration  due  to  centrifugal 
force,  while  this  tendency  to  move  outward  is  resisted  by  springs 
which  draw  the  weights  inward  as  the  speed  falls.  By  having 
an  initial  tension  upon  the  springs,  there  will  be  a  tendency  to 
equilibrium  between  the  centrifugal  action  and  the  springs  only 
at  that  speed  for  which  the  governor  is  adjusted.  The  governor 
may  either  be  on  the  principal  shaft  of  the  motor  or  on  a  sub- 
sidiary shaft,  driven  by  gears. 
By  this  latter  arrangement  the 
governor  may  be  placed  where 
convenient.  In  many  forms  the 
operator  of  the  engine  can  con- 
trol the  action  of  the  governor 
by  hand  as  a  means  of  varying 
the  speed  of  the  engine,  where  it 
may  be  desirable  to  do  so.  In 
Fig.  83,  for  example,  which  shows 
an  enlarged  detail  from  Figs.  51 
and  52,  /  and  /  are  the  masses 
thrown  radially  outward  by  the 
centrifugal  acceleration  due  to 
the  rotation  of  the  motor-shaft. 


FIG.  83. 


The  springs  R  tend  to  draw  them  in.  As  the  balls  or  weights  fly 
outward,  their  tendency  is  to  slide  the  collar  K  to  the  right,  while 
the  springs  R  will  slide  the  collar  to  the  left  when  they  pre- 
ponderate. The  bent-lever  arms  O  and  L  cause  this  motion  of 


266  THE  GAS-ENGINE. 

K  and  its  equilibrium  under  action  of  the  centrifugal  and  spring 
forces  to  adjust  the  amount  of  opening  of  the  throttle-valve  F 
in  the  pipe  through  which  energy  is  supplied  or  controlled  with 
respect  to  the  motor  cylinder.  The  long  upper  arm  M  can  be 
connected  by  a  rod  to  a  throttle-lever  at  the  operator's  hand,  so 
that  his  will  can  add  either  to  the  action  of  centrifugal  forces 
to  close  the  throttle-valve,  or  to  the  action  of  the  springs  R  to 
open  it.  The  sketch  of  course  applies  in  detail  to  only  one  sys- 
tem of  governing. 

136.  Governing  by  Missing  a  Charge.  The  Hit-or-miss 
Governor. — The  first  and  simplest  system  of  governing  was  to 
arrange  the  cam  by  which  the  inlet-valve  for  gas  was  raised  for 
the  suction  stroke  of  the  piston,  so  that  when  the  engine  was 
above  speed  this  cam  did  not  meet  the  lever  which  it  was  to  lift. 
The  engine,  therefore,  made  the  aspirating  stroke  without  draw- 
ing in  any  charge  of  gas,  and  of  course,  when  the  ignition  occurred, 
there  was  nothing  to  ignite.  In  some  early  forms  of  governor 
the  principle  of  inertia  was  applied  by  causing  a  reciprocating 
catch  which  should  normally  meet  the  end  of  the  valve-spindle, 
to  be  lifted  or  lowered  out  of  the  plane  of  that  spindle  by  the 
inertia  of  a  weight  attached  to  the  lever.  When  the  engine  was 
above  speed,  the  reciprocating  element,  moving  faster  than  the 
inertia  rate  of  the  weighted  ball,  caused  the  weight  and  attached 
lever  to  lag  behind  and  miss  connection  with  the  valve-stem. 

The  obvious  objection  to  this  system,  when  close  regulation 
is  demanded,  is  that  in  the  Otto  cycle  and  engine  the  missing  of  a 
working  stroke  results  in  an  inoperative  complete  cycle.  If  the 
load  suddenly  increases  just  after  the  charge  has  been  missed, 
there  will  be  a  notable  diminution  of  speed,  since  the  last  working 
stroke  took  place  two  revolutions  previous,  and  even  with  a  large 
weight  of  fly-wheel  the  variation  in  speed  could  not  fail  to  be 
detected.  Where  the  gas-engine  was  to  be  applied  to  incandes- 
cent electric  lighting,  or  to  other  purposes  where  close  regulation 
of  speed  was  a  vital  matter,  the  hit-or-miss  system  proved  unsatis- 
factory. It  has  still  beer  retained  on  some  automobile  practice, 


GOVERNING.  267 

in  order  that  when  the  motor  is  disconnected  from  the  trans- 
mission machinery,  and  the  motor-shaft  with  its  fly-wheel  is 
revolving  idly,  there  shall  be  no  unnecessary  consumption  of 
fuel  from  having  an  impulse  in  every  cycle  when  the  engine  is 
thus  running  light. 

137.  Governing  by  Impoverishing  the   Charge. — A  method 
of  governing  in  some  respects  analogous  to  the  foregoing,  and 
derived  from  it,  is  to  have  the  governor  act  to  reduce  the  pro- 
portion of  gas  in  the  charge  relatively  to  the  amount  of  air  on 
the  aspiration  stroke,  but  not  to  cut  off  the  supply  of  fuel  com- 
pletely.    This  will  result  in  having  an  inflammable  mixture  in 
the  cylinder  on  compression,  but  one  which  is  so  low  in  fuel  that 
the  stroke  is  a  comparatively  feeble  one  when  the  charge  is  ignited. 
This  governing  is  effected  by  having  a  cam  of  variable  section 
adjusted  on  the  shaft  by  the  position  of  the  governor- weights, 
so  that  the  gas- valve  is  held  open  a  less  proportion  of  the  suction 
stroke.     The  difficulty  with  this  system  is  that  the  inflammability 
of  the  mixture  is  so  widely  varied  by  the  proportion  of  gas  to  air 
that  it  may  easily  occur  that  with  a  given  compression  the  mix- 
ture will  fail  to  ignite  at  the  beginning  of  the  working  stroke, 
whereupon  a  charge  of  combustible  mixture  is  expelled  through 
the  exhaust  with  a  waste  of  fuel  and  a  possible  danger  of  its 
being  ignited  in  some  undesired  place.     This  system  has  been 
a  favorite  one  with  gasoline  machines  in  which  the  air  was  car- 
bureted by  aspirating  it  through  a  mixing  device.     If  the  gasoline 
vapor  was  not  ignited  in  the  cylinder,  it  might  be  ignited  by  the 
flame  in  the  next  subsequent  somewhat  violent  exhaust,  giving 
rise  to  explosions  in  the  exhaust-pipes  which  are  noisy  and  alarm- 
ing. 

138.  Governing  by  Throttling  the  Normal  Charge. — A  more 
judicious  system  than  the  preceding  is  to  cause  the  governor  to 
act  upon  both  the  air-  and  the  gas-inlet,  so  that  a  less  quantity  of 
the  normal  mixture  is.  drawn  into  the  cylinder,  but  the  propor- 
tions of  that  mixture  are  not  altered.     This  is  a  feature  of  the 
Westinghouse  engine  for  gas  (see  Fig.  36),  and  of  the  great  major- 


268 


THE  GAS-ENGINE. 


ity  of  the  newer  automobile  engines  which  receive  carbureted  air 
from  a  carburetor.  The  system  figured  in  Fig.  83  has  this  system 
in  view,  the  throttle-valve  being  between  the  carburetor  and  the 
motor.  See  also  Figs.  51  and  52.  It  has  the  advantage  that  there 
is  an  ignition  and  a  working  stroke  in  every  cycle,  but  that  the 
pressure  in  the  cylinder  is  less  by  reason  both  of  the  diminished 
compression  and  the  diminished  amount  of  fuel.  By  keeping 
the  mixture  in  constant  proportions  the  danger  of  failure  in  the 
ignition  is  lessened.  It  is  safe  to  say  that  the  advantages  offered  by 
this  system  are  so  great  that  the  tendency  in  design  is  to  make  use  of 
it  more  and  more,  either  exclusively  or  in  connection  with  the  meth- 
ods of  governing  by  cut-off  (par.  142)  and  by  ignition  shortly  to 
be  discussed.  It  avoids  the  difficulties  of  the  other  systems  and 
brings  the  governing  of  the  gas-engine  more  closely  into  parallel 
with  the  systems  used  in  the  steam-engine.  An  ingenious  system 
of  throttle-control  by  speed  has  been  applied  to  an  American  auto- 
mobile motor  (Winton,  Fig.  84).  A  rotary  air-pump  driven  by  the 


•     FIG.  84. 

motor  supplies  a  moderate  air-pressure  through  D  into  a  reservoir 
C.  Opening  from  this  is  a  cylinder  in  which  fits  the  piston  E. 
On  the  rod  of  the  latter  is  the  throttle-valve  F.  As  the  motor 
speeds  up,  the  pressure  rises  in  C  and,  overcoming  the  spring, 
closes  the  throttle  opening.  To  give  the  operator  control  over 
this  action,  an  outlet  from  C  is  controlled  by  a  push-button  and 
valve  at  A  and  G  under  the  heel  of  his  foot.  When  A  is  opened 


GOVERNING.  269 

wide  the  governing  action  is  practically  suspended,  since  the 
air-pressure  cannot  accumulate  in  C.  When  the  motor  is  stopped 
G  will  be  opened,  or  in  any  event  leakage  out  of  C  will  gradu- 
ally cause  the  throttle  to  open  wide,  so  that  when  the  start  is  to 
be  made  there  is  no  annoyance  from  reduction  of  pressure. 

139.  Governing  by  Throttling  the  Exhaust. — It  will  be  appar- 
ent that  the  net  work  of  the  working  stroke  in  a  multi-cylinder 
engine  can  be  reduced  and  a  braking  effect  in  a  single- cylinder 
engine  can  be  produced  if  the  free  discharge  of  the  products  of 
combustion  into  the  open  air  can  be  restricted  by  a  governing 
action  upon  the  opening  of  the  exhaust-valve.     This  throttling  of 
the  exhaust  operates  not  only  directly  to  diminish  the  net  forward 
or  driving  effort  on  the  crank-pin,  but  it  acts  to  leave  in  the  cylinder 
at  the  end  of  the  exhaust- stroke  a  certain  proportion  of  products 
of  combustion  which  are  confined  therein  and  which  must  expand 
by  the  aspirating  action  of  the  piston  down  to  and  below  atmos- 
pheric pressure  before  the  inlet- valves  for  gas  and  air  for  the  new 
charge  will  open.     The  aspiration  stroke,  therefore,  when  com- 
pleted, finds  the  cylinder  filled  in  part  with  neutrals  resulting 
from  the  throttled  exhaust  which  act  to  dilute  the  new  charge 
of  fresh  mixture.     This  action  is,  therefore,  in  effect  the  same 
as  that  of  throttling  the  normal  mixture  discussed  in  the  previous 
paragraph.     It  makes  a  hot  cylinder,  also,  from  the  compression 
of  the  hot  exhaust-gases.     This  same  action  results  if  the  exhaust- 
valve  is  opened  late  or  closed  early  in  the  exhaust  part  of  the  cycle 
and  during  the  exhaust- stroke. 

140.  Governing  by  Retarding   the  Ignition. — If  the  passage 
of  the  spark  between  the  points  of  the  sparking-plug  does  not 
occur  at  the  time  when  the  return  of  the  piston  for  its  compress- 
ing   stroke  has  produced  the  greatest  pressure  of  the  mixture 
in  the  compression  space,  but  takes  place  a  little  later,  after  the 
piston  has  begun  to  move  forward,  it  will  be  obvious  that  the 
igniting  of  that  mixture  will  not  produce  the  same  forward  effect. 
The  area  of  the  work  diagram  is  diminished  by  having  the  mix- 
ture at  the  beginning  of  the  working  stroke  retrace  the  curve  of 


27°  THE  GAS-ENGINE. 

+•*  • 

its  compression  before  the  ignition  raises  its  pressure  by  increas- 
ing its  temperature.  The  electrical  methods  of  ignition  are 
particularly  favorable  to  this  method  of  governing,  which  is  not 
possible  with  the  hot-tube  systems  nor  the  compression  plan. 

It  is  the  common  practice  to  adjust  the  normal  engine  to  fire 
its  charge  when  the  crank  is  about  15°  below  or  in  advance  of  its 
dead-centre.  This  lead  of  the  ignition  at  high  speed  particu- 
larly gives  a  chance  for  the  propagation  of  the  flame  at  constant 
volume  and  the  complete  establishment  of  pressure.  The  best 
mechanical  efficiency,  however,  favors  the  establishment  of  maxi- 
mum pressure,  after  the  piston  has  begun  to  move  forward  for 
its  working  stroke,  so  that  the  maximum  effect  should  not  be  so 
entirely  taken  up  on  the  shaft-bearings,  and  before  a  turning 
moment  has  been  created  for  the  crank.  That  is,  referring  to 
ig.  85,  if  the  angle  of  the  ignition  line  ab  is  inclined  to  the  ver- 


FIG.  85. — Ignition,  +$. 

tical  by  about  5°  or  6°.  If  the  ignition  be  retarded  by  delaying 
the  spark-instant,  the  ignition  line  becomes  more  inclined,  and 
the  maximum  pressure  comes  not  only  later,  but  by  the  expan- 
sion of  the  compressed  mixture  before  ignition  the  value  of  that 
maximum  is  less.  (Fig.  86.)  If  the  spark  is  still  further 
retarded,  the  diagram  of  effort  takes  the  shape  of  Fig.  87, 
which  is  from  a  6f  by  12  engine  at  240  revolutions,  with  the 
spark  timed  to  come  when  the  piston  is  J  of  an  inch  past  the 


GOVERNING. 


271 


dead- centre.     The  diagrams  are  scaled  to  show  the  fall  in  pres- 


sure. 


A  difficulty  with  this  system  of  governing  is  that  the  time  of 
the  stroke  after  ignition  may  not  be  long  enough  for  the  complete 
combustion  of  the  mixture  before  the  stroke  is  completed  and 
the  exhaust- valve  opens.  Hence  the  combustion  continues  into 
the  exhaust  passages  and  pipe,  with  waste  of  heat,  objectionable 


FIG.  86. — Ignition,  ±o. 


FIG.  87. — Ignition,  —  £. 

noise  due  to  the  pressure,  and  possible  exhaust  explosions.  If 
this  system  is  used  in  connection  with  the  plan  of  throttling  the 
mixture  of  the  normal  charge,  a  wide  range  of  speed  and  power 
control  may  be  easily  attained. 

The  retarded-ignition  principle  is  also  of  advantage  in  the 
manipulation  of  multiple-cylinder  engines  for  convenient  start- 
ing. If  the  spark  period  be  delayed  quite  late  or  the  circuit 
broken  when  the  motor  is  being  brought  to  rest,  it  may  result 
that  when  the  engine  stops  there  is  a  compressed  charge  in  one 
of  the  cylinders  ready  to  ignite,  but  which  has  not  been  fired. 
When  the  spark  is  passed  on  drawing  the  retarding  arrangement 


272  THE   GAS-ENGINE. 

back  toward  the  dead-centre  period,  this  compressed  charge  will 
be  fired  and  the  motor  start  without  the  necessity  for  hand 
starting  or  the  use  of  auxiliary  apparatus. 

141.  Governing  by  Advancing  the  Spark.  Pre-igniting  the 
Mixture. — If,  instead  of  timing  the -ignition-spark  after  the  work- 
ing stroke  has  begun,  the  charge  be  fired  before  the  compression 
stroke  is  completed,  and  more  than  normally  before  the  piston 
has  reached  its  dead- centre,  it  will  be  apparent  that  the  effect 
is  not  only  to  act  as  a  brake  upon  the  compression  stroke  and 
retard  the  engine,  but  also  to  diminish  the  effective  energy 
of  the  working  stroke,  since  the  ignition  takes  place  before 
the  compression  is  complete.  This  action  can  be  carried  to 
a  point  at  which  the  tendency  of  the  fly-wheel  and  crank  to 
produce  compression  shall  be  made  by  the  ignition  of  the 
charge  early  enough  to  have  a  leverage  sufficient  to  start  the 
crank  revolving  in  the  opposite  direction,  which  would  cause 
the  motor  to  make  a  backward  stroke.  This  is,  of  course, 
the  limit  in  such  pre-ignition  and  should  not,  under  ordinary 
circumstances,  be  allowed  to  occur.  Usually,  in  automobile 


FIG.  88. 

practice,  the  control  over  the  point  of  ignition  is  in  both  direc- 
tions and  on  each  side  of  the  normal  point,  so  that  at  the  will  of 
the  operator  the  ignition  may  be  retarded  or  put  forward.  Fig.  88 
shows  the  work  diagram  reduced  in  area  from  64  to  42  by  ad 
vancing  the  spark,  and  shows  the  form  of  diagrams  which 
result. 


GOVERNING. 


275 


142.  Governing  by  Cutting  Off  Admission. — A  system  of 
governing  has  been  used  by  Mr.  Chas.  E.  Sargent  whereby  the 
governing  effect  shall  be  to  cut  off  the  admission  of  mixture  when 
the  intake  stroke  is  only  partly  completed.  The  mixture  will 
be  rarefied  during  the  rest  of  the  stroke,  but  this  entails  no  loss,  as 
the  work  is  restored  upon  the  return  of  the  piston,  and  the  pres- 
sure is  restored  when  the  cut-off  is  reached  on  the  compression 
stroke.  Then  compression  begins  and  runs  through  the  remain- 
der of  the  stroke  only.  Hence  the  compression  is  varied  accord- 
ing to  the  work  to  be  done,  and  the  area  of  the  work  diagram. 


REV.   PER   MIN. 

220 

SPRING 

120      LB 

MAX.  COMP. 

fiO 

"       M.E.P. 

45.5 

MIN.  COMP. 

65 

"       M.E.P. 

26.4 

MAX.  RELEASE 

12 

MIN. 

2 

FIG.  89. 

varies  with  it.  Fig.  89  shows  a  number  of  superposed  strokes, 
and  the  governor  action  in  varying  the  cut-off  of  admission  and 
the  mean  effective  pressure.  Usually  the  ignition  is  made  to 
take  place  earlier  as  the  speed  tends  to  increase,  but  there  is  no 
loss  by  wire-drawing  due  to  throttling  effect.  The  terminal 
pressure  goes  down  with  this  system,  which  is  an  obvious  advan- 


274  THE   GAS-ENGINE. 

tage  as  respects  noise  from  the  exhaust.  This  cycle  in  modified 
form  has  been  proposed  by  Clerk  of  England,  Forest  of  France, 
and  Kohler  of  Germany.  It  bears  the  same  relation  to  the 
throttling  system  (par.  138)  as  the  automatic  cut-off  engine 
bears  to  the  throttling-engine  in  steam  practice.  It  is  a  system 
which  will  doubtless  prevail  more  and  more. 

143.  Governing  in  the  Two-cycle  System. — In  the  two- 
cycle  system  the  governing  by  throttling  the  exhaust  and  by  vary- 
ing the  points  of  ignition  is  not  as  simple  as  in  the  four- phase 
cycle.  The  fact  that  the  exhaust-ports  are  opened  by  the  motion 
of  the  piston  itself  at  the  completion  of  the  working  stroke  and 
are  closed  after  a  part  of  its  return  stroke  has  been  completed 
nearly"  always  leaves  a  proportion  of  the  products  of  combus- 
tion entrapped  in  the  cylinder,  so  that  exhaust  throttling  does 
not  apply  and  the  opening  of  the  exhaust-ports  before  the  end 
of  the  stroke  makes  the  retarded-ignition  method  unsatisfactory. 
Most  two-cycle  engines  throttle  the  mixture.  The  method  adopted 
in  the  Korting  engine  of  retarding  the  admission  of  the  constant 
mixture  until  part  of  the  compression  stroke  has  been  com- 
pleted is,  in  principle,  the  same  as  that  of  throttling  the  normal 
charge  in  combination  with  an  action  to  dilute  that  charge  with 
products  of  combustion  which  are  not  completely  expelled  when 
the  admission  of  fresh  mixture  is  retarded.  It  is  apparent  that 
combinations  of  the  methods  discussed  above  can  be  made  other 
than  those  which  have  been  described  as  actually  applied. 

144.  Limitations  of  the  Gas-Engine  by  the  Problem  of  Gov- 
erning. —  The  internal  combustion  engine,  whether  applied  to 
motor-cars,  launches  or  to  station  work  and  isolated  plants,  has 
the  same  problems  to  meet  respecting  its  uniform  motion  as  are 
to  be  met  when  power  is  taken  from  the  steam  engine.  Except 
in  the  launch  and  motor-car  the  requirement  is  usually  rigorous 
that  the  motion  of  the  crank  shall  be  so  nearly  uniform  per  stroke 
of  the  piston  that  all  revolutions  shall  be  made  in  equal  times, 
or  with  a  permitted  variation  therefrom  of  a  very  small  percentage. 
The  function  of  controlling  such  uniform  rotative  speed  is  divided 


GOVERNING. 


275 


between  the  fly-wheel  on  the  crank  or  motor  shaft  and  the 
governor. 

It  will  be  plain  that  absolutely  uniform  speed  of  rotation 
under  all  variations  of  resistance  and  effort,  and  under  the 
variations  of  the  forces  at  play  upon  the  crank-shaft  itself,  will  be 
very  difficult  of  practical  attainment.  A  governing  system 
which  would  do  this  would  be  called  isochronous,  or  equal 
timed,  making  the  motor  make  not  only  the  same  number  of 
strokes  per  second  or  per  minute  but  making  each  stroke  in  the 
same  time. 

The  forces  at  play  upon  the  crank-shaft  and  which  tend  to 
make  its  revolutions  non-isochronous  are  those  which  tend  to 
turn  it  in  its  normal  direction  or  revolution,  and  those  which 
retard  such  turning,  and  may  therefore  be  considered  to  act  as 
forces  in  the  opposite  direction.  On  the  positive  side  are: 

1.  The  effort  of  the  expanding  gas  mixture  upon  the  piston, 
acting  on  the  crank-pin. 

2.  The  inertia  or  stored  energy  in  the  reciprocating  masses 
attached  to  the  piston. 

3.  The  inertia  or  stored  energy  in   the  revolving  crank-arm, 
fly-wheel,  and  part  of  the  connecting  rod. 

Retarding  these  energies,  and  therefore  acting  in  opposite 
sense  are: 

4.  The   useful   resistances   being  overcome   reduced   to   the 
path  of  the  crank-pin. 

5.  The  resistances  in  the  cylinder  valves  and  passages  due 
to  the  compression  exhaust  and  aspiration  stroke. 

6.  The  mechanical  friction  of  the  engines  at  bearings  and 
contact  surfaces,  and  resistance  of  auxiliaries. 

7.  Inertia  of  reciprocating  parts  acting  to  retard  the  crank, 
and  possible  inertia  of  revolving  parts. 

These  have  been  more  exhaustively  analyzed  in  paragraph  ya, 
and  its  accompanying  diagram.  These  forces  cannot  be  con- 
stant in  any  case,  and  their  variations  will  be  due  to : 


276  THE  G4S-ENGINE. 

ia.  The  varying  effective  leverage  of  the  crank-arm,  from 
n  zero  at  the  inner  dead-centre  to  a  maximum  at  the  90°  point. 
Some  designers  have  aimed  to  secure  some  advantage  by  not 
putting  the  centre  of  the  crank-shaft  in  the  prolongation  of  the 
cylinder  axis,  but  have  " offset"  the  cylinder  to  get  better  work- 
ing angles  for  the  crank  on  the  power  stroke. 

ib.  The  pressure  of  the  expanding  gas  is  varying  all  through 
the  traverse. 

2a.  The  inertia  of  the  reciprocating  masses  is  only  acting 
positively  in  the  second  half  of  the  stroke.  In  the  first  half 
during  the  acceleration  period  they  are  retarding. 

30.  The  stored  energy  in  revolving  masses  is  only  liberated 
to  do  positive  work  when  the  crank-shaft  begins  to  slow  down 
from  excessive  resistance. 

The  resistant  forces  vary  because: 

40.  No  load  is  ever  constant.  Some  only  vary  more  than 
others  do. 

50.  These  vary  with  condition  of  the  air,  power  being  used, 
condition  of  motor  parts,  etc. 

6a.  Vary  with  care  in  lubrication,  quality  of  the  lubricant, 
conditions  of  the  feeding  apparatus. 

ya.  When  reciprocating  masses  must  be  accelerated  or  the 
fly-wheel  speeded  up,  the  inertia  of  these  must  be  overcome. 

When  there  are  several  cylinders  some  of  these  masses  may  be 
acting  in  opposite  ways  upon  the  crank,  and  these  influences 
will  go  through  cycles  of  increase  and  decrease. 

It  may  be  said  to  be  the  function  of  the  fly-wheel  to  take  care 
of  variations  per  stroke  or  revolution  in  Nos.  i,  2,  3,  5,  and  7. 
It  is  the  function  of  the  governor  to  take  care  of  Nos.  4  and  6, 
and  to  supply  sufficient  turning  force  to  meet  the  variations  in 
the  load.  A  massive  fly-wheel  may  also  act  as  an  accumulator 
for  turning  effort  under  sudden  variations  of  load,  but  when  such 
accumulation  is  used  up,  or  its  capacity  to  accumulate  is  reached, 
the  motor  slows  down  in  the  first  case,  and  speeds  up  in  the 
second.  The  governor  meets  variation  in  mean  effort  over 


GOVERNING.  277 

several  strokes;  the  fly-wheel  takes  care  of  maxima  and  minima 
of  effort  per  stroke  or  cycle.  The  governor  is  to  affect  the  area 
or  the  shape  of  the  indicator  diagram  from  which  mean  effective 
pressure  is  deduced;  the  fly-wheel  must  provide  for  cyclic  irregu- 
larities, inertia  effects,  and  part  of  the  sudden  variation  in  resist- 
ance for  a  very  short  time.  The  governor  itself  as  a  problem  in 
design  must  be  quickly  sensitive  to  the  retarding  or  accelerating 
effect  of  increase  or  decrease  in  the  external  resistance,  and 
must  quickly  thereafter  adjust  the  supply  of  energy  so  as  to 
modify  the  area  of  the  indicator  diagram  and  vary  the  mean 
effective  pressure.  Governors  which  are  massive  beyond  the 
needs  of  the  power  they  must  exert  to  affect  the  readjustment 
necessary,  will  be  sluggish  from  their  inertia,  and  will  have 
unnecessary  friction.  Both  will  make  the  governor  unsensitive. 
The  problem  of  governor  design  is  aside  from  the  present  pur- 
pose, but  it  may  be  said  in  general  that  governors  which  use 
springs  to  oppose  the  effect  of  speed  increases  are  more  quick- 
acting  than  those  which  depend  on  gravity. 

In  recent  applications  of  the  gas-engine  to  the  driving  of  electric- 
generators,  and  notably  of  alternators  in  parallel,  the  demand 
for  regulation  of  turning  effort  upon  the  fly-wheel  shaft  has  not 
only  been  for  an  isochronism  as  respects  numbers  of  revolutions 
per  minute,  but  further  than  this,  that  the  angular  variations  in 
each  stroke  or  revolution  shall  be  kept  inside  of  definite  limits. 
This  specification  demands  a  close  study  of  the  inertia  forces  in 
the  reciprocating  masses  and  the  securing  of  balance  of  effort  by 
the  arrangement  of  the  cylinders  relative  to  the  shaft,  and  the 
timing  of  the  impulse  strokes  which  together  shall  reduce  irregu- 
lar actions  per  stroke  to  a  minimum.  This  may  be  done  graph^ 
ically  from  a  combination  of  the  ordinates  of  gas  pressure,  with 
the  ordinates  of  the  inertia  forces,  and  a  resultant  curve  drawn, 
giving  a  force  curve.  On  the  latter  is  superposed  the  resist- 
ance curve,  supposed  constant  for  one  revolution  (or  for  two 
as  may  be  required)  and  from  the  two  is  derived  a  coefficient 
of  fluctuation  of  energy  per  period,  which  can  be  used  in  any  of 


278  THE  GAS-ENGINE. 

the  standard  deductions  for  fly-wheel  mass  in  accepted  formulae. 
The  study  of  balance  is  specially  important  in  design  of  motor- 
car engines  which  are  not  fastened  to  foundation  masses  as  in 
stationary  engines,  but  it  is  not  to  be  neglected  in  any  case. 
Students  are  referred  to  other  treatises  for  exhaustive  discussion.* 
It  is  obviously  difficult  in  the  single-cylinder  motor  operating 
with  the  four-phase  cycle  to  secure  a  uniform  torque  of  the 
engine-shaft,  even  with  a  massive  fly-wheel,  since  the  working 
impulse  comes  but  once  in  each  two  revolutions,  even  when 
the  resistance  is  constant.  This  difficulty  is  mitigated  by  in- 
creasing the  number  of  the  cylinders  up  to  four,  so  that  there 
shall  be  an  impulse  at  each  half-revolution,  as  occurs  with  the 
double-acting  single-cylinder  steam-engine.  It  is  also  made  of 
less  consequence  by  greatly  increasing  the  speed  of  the  fly-wheel 
shaft  so  that  the  interval  of  time  between  impulse  strokes  shall 
be  correspondingly  lessened  and  the  resistance  attacked  by  the 
impulse  stroke  with  correspondingly  greater  frequency.  For 
these  reasons  the  limitations  set  to  the  use  of  the  single-cylinder 
four-phase  cycle  where  uniform  speed  of  rotation  was  demanded 
have  been  to  a  great  extent  removed.  It  remains  the  fact,  how- 
ever, that  even  the  best  methods  of  governing  have  not  yet  pro- 
duced such  nicety  of  adjustment  of  the  working  pressure  to  the 
resistance  as  is  possible  with  the  automatic  cut-off  steam-engine 
in  view  of  the  practical  impossibility  of  adjusting  the  release  of 
energy  in  the  stroke  within  the  narrower  limits  imposed  by  the 
rate  at  which  this  energy  is  released  when  the  charge  is  ignited. 
The  steam-engine  draws  from  a  reservoir  of  accumulated  pres- 
sure, and  may  draw  more  or  less  as  required  per  stroke.  The 
internal-combustion  system  must  receive  all  the  energy  resident 
in  the  mixture  received,  and  can  only  govern  by  varying  this 
amount  of  energy  before  it  is  released. 

*  For  example,  "Gas  Engine  Design,"  pp.  61-146.      C.   E.  Lucke.     Van 
Nostrand  Co.,  1905. 


CHAPTER  XIII. 
THE   COOLING  OF    THE   CYLINDER. 

145.  Introductory. — Since    the    effective    utilization    of    the 
heat  energy  in  an  internal-combustion  motor  depends  upon  the 
difference  between  the  initial  and  final  temperatures  of  the  mix- 
ture which  drives  the  piston,  it  will  be  apparent  that  the  ideal  and 
economic  method  for  cooling  the  gas  would  be  the  effective  trans- 
fer of  all  of  its  sensible  heat  into  mechanical  work.    It  is  desirable 
that  the  gas  should  thus  be  cooled  in  order  that  it  may  carry  out 
to  waste  the  minimum  amount  of  available  energy.     On  the  other 
hand  the  metal  of  the  cylinder  should  be  cooled  not  only  as  a 
matter  of  comfort  to  those  who  are  about  it,  but  to  prevent  defor- 
mations, leaky  valves,  defective  alignment,  and  oxidation  resulting 
from  high  heat.     It  will  be  apparent,  furthermore,  that  the  cool- 
ing of  the  metal  must  be  done  with  convenient  means  and  without 
requiring  too  great  bulk  or  weight  of  the  medium  used  for  cooling. 

It  may  be  said,  in  general  terms,  that  there  are  -  two  methods 
of  cooling  the  metal.  One  is  by  the  use  of  water  and  the  other 
by  the  use  of  air.  For  the  cooling  of  the  gas  one  method  will 
be  by  water  injection  and  the  other  will  be  by  jacket-cooling 
through  the  metal  walls  of  the  cylinder.  The  water  may  be 
most  effectively  used  upon  the  mixture  by  injecting  it.  The  water 
or  air  cooling  of  the  metal  will  be  done  by  circulation. 

146.  Cooling  by  Injection  into  the  Air,  into  the  Expanded 
Gases,  into  the  Products  of  Combustion. — It  has  been  proposed 

to  inject  into  the  air  which  is  drawn  into  the  cylinder  on  the  aspi- 

279 


280  THE  GAS-ENGINE. 

ration  stroke  a  certain  quantity  of  water  in  the  form  of  mist.  The 
compression  of  the  mixture  which  raises  its  temperature  will 
convert  this  finely  divided  water  into  steam,  which  will  partake 
of  the  heating  when  the  gas  ignites  and  by  its  higher  specific  heat 
shall  tend  to  keep  the  temperature  of  the  mixture  lower  than  it 
would  be  in  the  absence  of  such  water.  The  water  partakes 
of  the  cooling  due  to  the  adiabatic  expansion,  but  the  heat  to 
vaporize  it  when  the  pressure  is  lowered  at  the  opening  of  the 
exhaust  will  be  absorbed  from  the  products  of  combustion,  where- 
by their  temperature  will  be  lowered. 

A  variant  upon  this  plan  is  to  inject  the  water  in  spray  into 
the  expanded  gases  after  the  ignition  has  taken  place,  with  the 
idea  that  the  steam  thus  formed  should  partake  of  the  expansion 
in  the  cylinder  and,  by  the  absorption  of  the  heat  for  the  vapori- 
zation, cool  the  mixture  as  in  the  foregoing  method. 

The  difficulty,  so  far  as  both  systems  are  concerned,  is  that 
the  injection  of  this  spray  or  mist  of  water  with  its  higher  specific 
heat  tends  to  lower  the  temperature  in  the  cylinder  and  thus  to 
diminish  the  net  forward  effect  upon  the  piston;  and  to  be  effect- 
ive enough  to  render  a  water-jacket  unnecessary  the  quantity 
of  injection  water  required  would  render  combustion  impossible, 
by  reason  of  the  great  dilution  by  water-vapor  and  spray.  If 
little  water  is  injected,  so  that  this  effect  is  not  produced,  the 
water  does  little  cooling,  but  in  any  case  its  effect  is  to  diminish 
the  area  of  the  work  diagram  in  the  cylinder. 

Injection  has  also  been  practised  as  respects  the  products  of 
combustion  after  they  have  left  the  cylinder  and  are  in  the  ex- 
haust-passage. This  lowers  the  tension  of  the  exhaust-gases  by 
lowering  their  temperature,  but  produces  no  effect  upon  the 
medium  which  is  working  in  the  cylinder  itself.  It  is  not,  there- 
fore, usually  worth  while  to  pay  much  attention  to  the  heat  in 
these  products  of  combustion,  since  it  is  inconvenient  to  utilize 
it  in  any  practical  way. 

147.  Cooling  of  Metal  by  a  Water-jacket,  the  Steam  to  be 
Utilized  or  Wasted. — Since  the  specific  heat  of  water  is  unity, 


THE  COOLING  OF  THE  CYLINDER.  281 

it  is  the  most  convenient  medium  to  use  for  withdrawing  excess 
of  heat  from  the  metal  of  the  cylinder  and  its  valves.  This  is 
usually  accomplished  by  casting  the  cylinder  with  double  walls 
or  by  surrounding  it  with  a  brazed  copper- jacket  and  circulating 
the  cooling  water  through  the  hollow  spaces.  The  cool  water 
enters  at  the  bottom  and,  becoming  warmed,  it  flows  off  at  the 
top,  carrying  with  it  any  bubbles  of  steam  which  may  form  in 
the  process,  and  which  would  have  a  tendency  to  rise.  If  there 
is  an  abundance  of  water,  it  is  usually  convenient  to  waste 
the  heated  water  without  attempting  to  apply  it  to  any  useful 
purpose.  If  water  is  limited,  as  in  the  case  of  the  automobile 
engine,  it  will  be  necessary  to  use  some  means  for  cooling  it  in 
some  form  of  radiator,  whereby  the  heat  which  it  absorbs  in  cir- 
culating around  the  cylinder  shall  be  withdrawn  and  the  same 
water  used  over  and  over  again.  It  is  possible  to  utilize  the  heat 
which  the  water-jacket  will  carry  away,  but  ordinarily  this  is 
more  trouble  than  the  economy  which  it  represents. 

In  the  automobile  water-cooled  engine  the  radiator  for  cool- 
ing the  heated  water  is  made  of  a  coil  of  pipes,  each  pipe  being 
armed  with  a  very  large  external  radiating  surface  so  that  the 
movement  of  the  vehicle  through  the  air  shall  give  to  the  latter 
a  great  surface  upon  which  to  act  for  the  withdrawal  of  the  heat 
of  the  pipe  (see  par.  87).  Some  forms  of  radiator  have  trans- 
verse cooling  pipes  through  the  main  body  of  the  water,  and  in 
addition  to  the  motion  of  the  vehicle  through  the  air  a  further 
current  of  air  is  stimulated  by  a  propeller  fan  driven  from  the 
engine,  so  that  the  velocity  of  the  motor-shaft  shall  determine  the 
volume  of  cooling  air  and  not  alone  the  velocity  of  the  car. 

It  is  usual  to  let  the  cooling  water  reach  nearly  the  boiling- 
point,  or  about  180°  Fahr.,  so  as  to  keep  the  metal  below  the 
point  of  deformations,  and  yet  not  cool  the  cylinder- walls  unduly. 
If  the  water  boils,  of  course  it  gradually  dissipates  as  vapor  and 
must  be  replaced.  About  one  gallon  of  water  per  horse-power 
seems  to  be  a  convenient  proportion  for  the  tanks  which  carry 
the  cooling  water.  In  cold  climates  care  has  to  be  taken  in  the 


282  THE  GAS-ENGINE. 

cooling  of  out-of-door  motors  lest  the  cooling  water  freeze  when 
the  motor  is  at  rest.  This  has  resulted  in  the  mixing  of  glycerine 
with  the  water  in  equal  parts,  or  the  adding  of  chloride  of  cal- 
cium (CaCl2)  till  the  solution  has  a  specific  gravity  of  1.20. 
Such  a  solution  will  not  freeze  at  15°  below  zero  Fa'hrenheit. 
Trouble  has  often  been  experienced  with  water-cooled  motors 
which  use  water  containing  mineral  matter,  from  the  deposit  of 
such  scale- forming  material  in  the  jackets.  The  narrow  spaces 
become  clogged  with  the  deposits,  and  the  water  cannot  get  access 
for  cooling  the  metal. 

148.  Water-cooling  of  the  Piston. — While  the  surrounding  of 
the  cylinder-walls  by  circulating  water  in  the  water-jacket  has 
a  tendency  to  keep  their  metal  cool,  it  does  not  affect  the  recip- 
rocating piston  which  touches  these  walls  over  a  comparatively 
narrow  surface  while  exposed  to  the  high  temperature  of  the 
charge  over  the  large  area  of  its  head.     This  has  necessitated, 
in  engines  of  large  size,  that  provision  be  made  for  cooling  the 
piston  by  circulating  water  through  hollows  cast  in  its  structure. 
This  is  shown  to  be  necessary  by  the  fact  that  even  when  the 
sides  are  water- jacketed   the   pistons  of   large  gas-engines  will 
appear  red  to  the  eye  in  the  dark,  in  the  absence  of  such  inner 
circulation.     The  water  is  introduced  either  by  means  of  a  flexi- 
ble connection  or  by  means  of  two  hollow  tubes,  finished  on  the 
outside,  which  slide  through  a  stuffing-box,   entering  into  cor- 
responding chambers  within  one  of  which  cool  water  is  main- 
tained under  pressure  and  through  the  other  of  which  the  heated 
water  is  discharged. 

149.  Cooling  by    Air-jacket.  —  The  inconvenience  of  carry- 
ing the  necessary  weight  of  cooling  water  in  the  automobile,  and 
the  annoyance  which  is  offered  in  winter  by  the  presence  of  this 
water,  and  the  danger  of  its  freezing  in  cold  weather,  when  the 
engine  is  not  in  operation,  have  brought  about  the  design  called 
the  air-cooled  motor.     The  cylinders  of  such  engines  are  cast 
with  deep  corrugated  exterior  surfaces  or  are  fitted  with  a  multi- 
tude of  radial  screwed  pins  on  the  outside  so  that  for  a  given 


THE  COOLING   OF   THE   CYLINDER.  283 

diameter  of  cylinder  a  very  much  increased  external  surface  shall 
be  presented  to  the  cooling  action  of  the  air,  both  by  radiation  and 
contact.  This  effect  may  be  increased  by  a  fan  action  which  shall 
blow  air  upon  the  radiating  surface  of  the  cylinder  and  tend  by 
this  action  to  keep  it  cool.  Such  cylinders  are,  of  course,  heavier 
than  the  water-cooled  cylinder,  but  the  weight  of  the  water  is 
avoided.  Fig.  50  shows  a  characteristic  structure  of  such  air- 
cooled  cylinders  (see  also  par.  87).  The  limitation  in  air- 
cooling  seems  to  be  set  by  the  quantity  of  heat  in  units  which 
is  liberated  on  the  working  stroke.  As  the  engine  grows  more 
powerful,  the  difficulty  of  effective  cooling  increases,  and  is  set  at 
not  far  from  ten  horse-power  at  present,  by  the  fact  that  enough 
air  cannot  be  brought  into  action  in  the  limited  surface  to  cool 
a  cylinder  heated  hot  by  a  large  weight  of  fuel.  If  the  cylinder 
is  not  adequately  cooled,  the  compression  of  the  charge  may  result 
in  pre-ignitions  or  back-firing,  and  difficulty  may  be  experienced 
in  stopping  it  quickly  without  inconvenient  use  of  powerful  brakes 
(see  par.  127). 

150.  The  Circulation  of  the  Cooling  Water  and  the  Amount 
Required  for  Cooling. — In  automobile  practice  it  has  been  ob- 
served that  it  is  usual  to  proportion  the  surface  of  the  radiator 
so  that  the  temperature  of  the  cooling  water  shall  rise  nearly 
to  the  boiling-point.  If  it  were  to  be  allowed  to  get  hotter  than 
this,  the  water  would,  of  course,  generate  steam,  which  would 
produce  a  pressure  upon  surfaces  ill  adapted  to  resist  pressure 
and  which  would  result  in  a  dissipation  of  the  water  in  the  tanks, 
requiring  its  frequent  renewal.  This  circulation  of  the  water 
through  the  jacket  and  the  radiator  is  accomplished  by  a  pump 
either  of  the  centrifugal  or  rotary  type  in  most  cases,  since  a  small 
volume  or  weight  of  pump  of  this  design  will  circulate  the  great- 
est weight  of  water  with  the  small  resistance  which  such  circu- 
lation offers.  The  weight  of  water  which  is  to  be  circulated  to 
keep  a  given  weight  of  metal  at  a  certain  fixed  temperature  is 
given  by  a  simple  equation  for  the  transfer  of  heat  involving  the 
temperatures,  specific  heats,  and  weights.  If  W  be  the  weight 
of  the  iron  to  be  cooled,  and  its  specific  heat  Q,  and  the  range 


284  THE  GAS-ENGINE. 

of  temperature  through  which  it  is  to  be  cooled  be  denoted  by 
/J-/2,  while  for  water  the  weight  be  designated  by  wt  specific 
heat  by  unity,  and  its  range  of  temperature  t2  —  /3,  since  the  water 
and  the  iron  will  be  assumed  to  have  practically  the  same  tem- 
perature when  the  latter  has  been  cooled,  the  equation  will  appear 


In  this  equation  the  temperatures  are  known  or  assumed 
and  the  unknown  quantity  to  be  calculated  is  w,  when  the  other 
elements  of  the  equation  are  known. 

It  should  be  carefully  observed  in  designing  water-jackets  that 
the  different  parts  of  the  cylinder  casting  are  not  exposed  to  the 
same  intensity  of  heating  effect.  Hence  the  consequences  of 
distortion  from  unequal  heating  and  disproportionate  cooling  are 
as  carefully  to  be  guarded  against.  The  parts  should  be  free 
further  to  expand  and  contract  under  the  changes  of  heat  without 
distortions  of  other  parts.  Valve-seats  in  particular  are  points 
of  special  importance,  and  a  design  of  much  merit  will  be  one  in 
which  both  seat  and  stem  are  formed  in  cored  castings  around 
which  a  copious  flow  of  cooling  water  can  be  secured.  Such 
cooling  also  prevents  a  previous  dilation  of  the  mixture  by  heat 
on  entering  the  admission-valve,  whose  consequence  will  be  a  loss 
of  weight  in  a  volume  of  given  dimensions.  It  is  best  to  cool 
the  valve-casings  first  and  with  the  coolest  water;  the  warmed 
water  may  pass  thence  to  the  cylinders  and  so  to  waste. 


CHAPTER  XIV. 

THE  COMBUSTION-CHAMBER  AND  THE  EXHAUST. 

151.  Introductory. — In  the  steam-engine  and  in  the  air- 
compressor  it  is  desirable  that  the  space  between  the  head  of 
the  piston  and  the  head  of  the  cylinder  should  be  reduced  to  the 
lowest  possible  percentage  of  the  volume  swept  through  by  the 
piston.  This  is  by  reason  of  the  fact  that  this  volume  in  the 
steam-cylinder  is  filled  at  each  stroke  by  steam  from  the  boiler 
which  is  not  required  to  do  the  work  of  that  stroke  and  which 
is  exhausted  with  the  working  steam  when  the  exhaust-valve  is 
opened.  In  the  air- compressor,  whatever  compressed  air  re- 
mains in  this  clearance  volume  expands  during  that  stroke  which 
should  be  entirely  the  admission  stroke  for  fresh  air,  and  by  its 
expansion  precludes  the  opening  of  the  inlet-valves  until  the  pres- 
sure in  the  cylinder  is  less  than  the  atmospheric  pressure  without. 
In  the  gas-engine,  on  the  other  hand,  the  space  between  the  pis- 
ton and  the  end  of  the  cylinder,  when  the  engine  is  on  its  inner 
dead-centre,  is  the  space  in  which  the  combustible  mixture  is  to 
be  held  under  compression  from  the  return  stroke  of  the  piston, 
and  which  must  contain  a  sufficient  amount  of  the  combustible 
mixture  to  furnish  whatever  effective  pressure  is  to  be  exerted 
when  the  charge  is  ignited.  It  will  be  apparent,  therefore,  that 
the  volume  of  this  clearance  space  is,  in  effect,  the  combustion- 
chamber  of  the  engine,  and  it  must  bear  such  a  relation  to 
the  volume  of  the  piston  displacement  as  shall  give  the  desired 
compression  pressure  at  the  moment  that  the  charge  is  to  be 

285 


286 


THE  GAS-ENGINE. 


fired,  under  normal  conditions.    What,  then,  should  be  the  volume 
of  the  combustion- chamber  ? 

152.  Volume  of  the  Combustion-chamber. — The  volume 
of  the  combustion-chamber  will  be  very  greatly  dependent  upon 
the  quality  of  the  fuel  which  is  to  be  burned  in  the  engine.  While 
the  greater  the  pressure  caused  by  the  compression,  the  greater 
work  will  be  done  in  the  Otto  cycle,  a  definite  limit  is  set  with 
rich  mixtures  which  are  readily  ignited.  With  gasoline  gas, 
for  instance,  it  is  impossible  to  carry  the  compression  above  80 
pounds  per  square  inch,  since  the  heat  generated  by  the  com- 
pression within  these  limits  will  be  sufficient  to  pre-ignite  the 
charge,  causing  the  piston  to  make  a  back  stroke.  With  lean 
mixtures,  such  as  blast-furnace  gas,  the  compression  pressure 
may  be  made  much  greater  than  this,  without  danger  of  pre- 
ignition.  The  following  table  gives  some  data  concerning  the 
limits  of  pressure  with  combustibles  of  different  points  of  ignition : 

COMPRESSION    PRESSURES    IN    POUNDS    PER   SQUARE    INCH. 

Pressures   Permissible  When  Fuel  Used  is 


Type  of  Engine. 

Blast 
Furnace 
Gas. 

Producer 
Gas. 

Natural 
Gas. 

City  or 
lllum'tg 
Gas. 

Gaso- 
line. 

Kero- 
sene. 

Alcohol. 

1 

Large  size 
Rich  gas  

2 

I2O 

3 

TOO 

4 

5 

60 

6 

7 

8 

Lean  gas 

IQO 

1  60 

1  3O 

IOO 

Average                          ( 

I  ^O 

I  -2  r 

1 
Small  size                          .  . 

155 

140 
I2C 

US 
60 

80 

(  low  

6< 

4C 

jr 

I  OO 

High  speed  <  high  
(  average    .  .  . 
C  low  
Low  speed  <  high 

9° 
80 

95 
80 
60 

8c; 

85 
65 

200 
!50 

.     (  average  

70 

If  the  piston  be  assumed  to  draw  in  one  pound  of  the  mixture 
of  fuel  and  air  at  atmospheric  pressure  when  it  has  moved  to  its 
extreme  position  (called  A  in  Fig.  205),  and  such  initial  volume 
Vi  be  assumed  to  have  its  weight  unaffected  by  the  presence  of 
the  gasefied  fuel,  it  may  be  supposed  to  occupy  the  same  volume 


THE  COMBUSTION-CHAMBER  AND    THE  EXHAUST.          287 

at  62°  F.  as  the  same  weight  of  air  would.  In  paragraph  n 
the  volume  at  32°  F.  was  called  12.39  cubic  feet;  hence  at 
62°  F.,  by  the  Mariotte  law  (par.  43),  its  volume  will  be : 

{*  ry  2 

Vt  =  - —  X  12.39  =  I3-I33   cubic  feet. 

If  this  initial  volume  vt-  be  compressed  to  any  other  volume  Vx,  or 
to  a  final  volume  Vf,  and  the  corresponding  pressure  be  assumed, 
the  value  will  be  given  when  the  cylinder  walls  do  not  carry  off 
any  of  the  heat  due  to  such  compression  by  the  formula  of  para- 
graph 51,  in  which  the  initial  pressure  is  that  of  the  atmosphere, 
or  14.7  pounds  per  square  inch,  and  the  exponent  n  =  1.41. 
Hence 


13-13 

or, 


C0 


The  table  on  following  page  gives  the  computation  of  such  volumes 

p 
with  assumed  ratios  of  — -  in  atmospheres  in  order  to  make  the 

*  X 

numerator  unity  for  convenience  in  graphical  representation,  as 
well  as  in  pounds  per  square  inch. 

A  graphical  presentation  of  the  results  of  computation  as  given 
in  column  4  of  the  foregoing  table  appears  in  Fig.  257  herewith, 
which  is  the  standard  curve  for  adiabatic  air  compression,  and 
if  used  as  a  template  may  be  applied  to  actual  indicator  cards  by 
superposing  the  template  pressure  over  that  realized  actually  in 
the  card  under  observation  to  find  the  volume  ratio,  or  the 
volume  ratio  being  known  the  pressure  theoretical  for  these 
volumes  may  be  read  directly. 

But  the  foregoing  discussion  concerning  the  pre-ignition 
difficulty  with  the  various  fuels,  and  the  appropriate  compression 
pressure  indicates  that  the  compression  pressure  ratio  cannot  be 


288 


THE  GAS-ENGINE. 


COMPUTATION  TABLE   OF   VOLUME   RATIOS    IN    COMPRESSION 
WHEN   PRESSURE   RATIOS   ARE   TO    BE   ASSUMED. 


Compression 
in 
Atmospheres. 

Pounds  per 
Square  Inch. 

Value  of 

(£)"' 

Computed. 

Resulting 
Volume  Vx 
in  Cubic  Feet. 

Value  of 
(P*\  29 
\Pl) 
Computed. 

Value  of 

-[•-(?r 

Computed. 

i-5 

22.05 

0.881 

"•57 

2.0 

29.40 

.611 

8.02 

. 

2-5 

36-75 

•5217 

6.85 

. 

3-° 

44.10 

.458 

6.01 

0.727 

1.474 

3-5 

51-45 

.411 

5-39 

4.0 

58.80 

•374 

4.91 

.669 

1.787 

4-5 

66.15 

•343 

4-5° 

5-° 

73-5° 

•3i9 

4-19 

[627 

2.014 

5-5 

80.85 

.298 

3-9i 

6.0 

88.20 

.28! 

3-69 

•595 

2.187 

6-5 

95-55 

.265 

3-48 

.  .  . 

7.0 

102  .90 

•251 

3-29 

•569 

2.327 

7-5 

no.  25 

•239 

3-n 

8.0 

1  1  7  .  60 

.228 

2-99 

•547 

2.446 

8-5 

124.95 

.219 

2.875 

9.0 

132.30 

.209 

2.74 

•527 

2-554 

9-5 

139-65 

.202 

2.65 

IO.O 

147.00 

•195 

2.56 

•5i3 

2.630 

10.5 

J54-35 

.188 

2.47 

II.  0 

161  .  70 

.182 

2-39 

'498 

2.711 

«-s 

169.05 

.177 

2-33 

, 

12.  O 

176.40 

.171 

2.245 

.486 

2-775 

I2-S 

183-75 

.166 

2.18 

10 


45678 
Volumes  in  Cubic  Feet 


10         11         12        13 


FIG.  257. 


THE  COMBUSTION-CHAMBER  'AND    THE  EXHAUST.          289 

arbitrarily  assumed,  but  must  be  based  on  the  characteristic  of 
the  fuel  in  this  respect.    . 

A  second  underlying  principle  for  design  will  be  to  work  back 
from  the  mean  effective  pressure  desired.  In  paragraphs  40 
and  47  it  was  developed  that 


an  equation  which  involves  the  ratio  of  the  final  to  the  initial 

pressures  resulting  from  the  compression  process,  when  H  is  the 

calorific  power  or  heating  value  of  the  fuel.     In  column  5  of  the 

preceding  table  are  given  the   computed   values  for  the   factor 

p 

^~  and  in   column    6    the  result   of    multiplying   the  efficiency 

factor  by  5.41.  This  column^can  therefore  be  used  by  inserting 
in  the  formula 

M  E  P  H     ftabular  value 

a  +  i  |_irom  column  6. 

the  value  appropriate  for  the  compression  which  is  proper  for 
that  fuel,  and  checking  the  result  of  this  substitution  with  the 
value  for  M.E.P.  which  has  been  used  in  working  out  the  H.P. 
To  use  this  effectively,  however,  and  to  pass  from  the  theoretical 
results  with  standard  conditions  to  those  of  practice,  a  knowledge 
should  be  available  of  the  values  for  M.E.P.  with  various  com- 
pression values  as  realized  in  engines  at  work  and  using  the 
various  fuels.  The  following  table  gives  some  of  these  data, 
but  while  all  are  from  tests,  it  does  not  follow  that  all  are  from 
tests  under  the  best  combinations  of  condition.  It  will  be  con- 
venient to  have  the  data  of  this  table  greatly  extended  by  series 
of  tests  under  identical  fuel  conditions  with  a  given  engine,  and 
with  different  engines.  The  lack  of  concurrence  in  the  series 
indicates  the  need  of  further  research,  and  the  care  and  experi- 
ence which  must  be  the  guides  in  use. 


290 


THE  G4S-ENGINE. 


Compressions 
Pounds  per 
Square  Inch 
Absolute. 

Mean  Effective  Pressure  Observed  when  Fuel  is 

Blast 
Furnace 
Gas. 

Producer 
Gas. 

Natural 
Gas. 

City  or 
Illuminating 
Gas. 

Gasoline. 

Kerosene. 

45 

45 

46 

40 

So 

35 

11 

'So 

85 

63 

69 

65 

68 

66 

95 

106 

68 

.  .  . 

40 

70 

60 

75 

72 

75 

IOO 

86 

70 

86 

72 

90 

'62 

Qi 

9 

o 

95 

90 

< 

5o 

95 

IOO 

103 

63 

1  08 

88 

US 

103 

125 

5i 

'68 

130 

82 

i35 

9° 

. 

140 

47 

83 

.  .  . 

. 

155 

81 

. 

170 

73 

• 

A  third  principle  of  design  is  that  of  which  an  example  is 
given  in  paragraph  203,  in  which  the  actual  value  of  n  as  dis- 
cussed in  paragraph  56  for  the  compression  stroke  is  taken  as 
1.35  to  allow  for  the  action  of  the  cylinder  walls  and  other  trans- 
fers of  heat.  If  as  before  and  in  Fig.  20.5  the  initial  volume 
before  compression  be  called  V{  =  piston  displacement  +  clear- 
ance volume,  Vf  =  final  volume  =  clearance  volume  only;  then 
V{  -  Vf  =  piston  displacement,  and  if  R  be  the  ratio  between 
the  clearance  volume  and  the  piston  displacement : 


Vf  clearance  volume  i 

V-t  —  Vf~~  piston  displacement  ~~  V\ 

v,    ' 


=  R. 


THE  COMBUSTION-CHAMBER  AND    THE  EXHAUST.          291 
If  thsn  as  in  paragraph  56  it  be  taken  that  : 


r,    j-    =\f 

and  these  pressures  be  substituted  for  the  volumes  in  the  equation 
for  R,  and  the  appropriate  values  for  the  former  be  inserted  the 
values  result; 


For  street  -gas 


For  producer-gas 


For  the  Diesel  high  compression 


From  these  derivations  the  origins  of  the  usual  values  are 
made  to  appear.  When  the  builder  does  not  know  what  fuel 
is  to  be  used,  but  is  obliged  to  make  a  commercial  article  which 
will  not  be  too  far  amiss  for  any  ordinary  case,  he  selects  the 
middle  of  the  series  and  a  mean  value.  This  explains  the  very 
general  adherence  to  about  30  per  cent. 

It  will  be  apparent,  from  the  foregoing  equations  and  discus- 
sions, that  the  less  the  clearance  volume  with  a  given  displace- 
ment volume,  the  higher  the  compression  pressure.  To  guard 
against  pre-ignitions,  this  will  compel  a  leaner  mixture,  or  one  with 
less  fuel  in  proportion  to  air,  and  as  the  fuel  is  the  costly  element, 
the  greater  will  be  the  fuel  economy  for  a  given  displacement 
volume.  But  further  than  this,  a  diminished  clearance  volume 


292  \  THE  G4S-ENGINE. 

gives  a  less  volume  of  burnt  gases  to  be  admixed  with  the  fresh 
charge,  and  to  dilute  it  so  as  to  diminish  the  effective  weight  of 
fuel.  This  diminished  dilution  will  lessen  the  percentage  of 
neutral  gas  with  its  effect  on  combustion  (par.  222).  With  a  small 
clearance  the  cylinder  volume  is  more  effectively  scavenged  when 
the  exhaust  opens. 

153.  Form  of  the   Combustion -chamber.  —  It  is   desirable 
for  reasons  of  strength  and  simplicity  in  casting  that  the  combus- 
tion-chamber be  of  rounded  or  spheroidal  form,  with  no  corners 
or  pockets  in  its  volume.     The  openings  leading  to  the  valves 
for  similar  reasons  should  open  small  vestibules  into  the  combus- 
tion-chamber, so  that  .the  gas  in  these  entries  may  partake  of 
the  facility  of  ignition  belonging  to  the  main  volume  of  mixture. 
It  has  been  found  that  some  very  curious  phenomena  result  from 
such  a  shape  of  the  combustion  volume  behind  the  piston  as  shall 
make  the  ignition  of  the  mixture  resemble  a  succession  of  explo- 
sions.    When  these  shapes  of  the  combustion-chamber  and  its 
entries  are  conducive  to  this  action,  there  are  developed  pulsations 
In  the  mass  of  gas  which  seem  to  be  curiously  cumulative  in  effect 
and  which,  when  the  right  proportions  are  attained,  reach  an 
intensity  close  to  the  limit  of  the  possibility  of  their  being  resisted 
by   the   metal.     These   pulsations   reveal   themselves,   often,    to 
the  indicator-card  by  a  succession  of  waves  in  the  line  of  expan- 
sion which  would  naturally  be  attributed  to  inertia  of  the  indi- 
cator-piston and  attached  parts,  but  which  can  be  proved  to  be 
the  result  of  this  pulsating  action  by  the  very  simple  experiment 
which  is  described  in  paragraph  204  of  Chapter  XIX,  to  which 
the  student  is  referred. 

154.  Disposal  of    the    Exhaust-gases. — The    exhaust   from 
the  cylinder  should  be  mainly  carbonic  acid  gas,  steam,  and  air. 
With  the  gasoline  engines  there  may  be  present  a  certain  amount 
of  hydrocarbon  gas  incompletely  burned,  which  will  give  a  slight 
color  to  the  exhaust  with  a  characteristic  odor.     In  damp  weather 
the  exhaust  also  may  contain  a  little  steam  from  the  moist  air 
drawn  into  the  cylinder  and  there  made  into  steam  to  appear 
in  the  cooled  exhaust  in  visible  form.     The  requirement  in  many 


THE  COMBUSTION-CHAMBER  AND    THE  EXHAUST.          293 

cities  for  stationary  practice  is  that  the  exhaust-pipe  from  the 
engine  must  first  discharge  into  a  reservoir  or  pot  from  which  the 
exhaust-pipe  proper  shall  pass  out  and  shall  be  carried  continu- 
ously through  the  chimney  or  flue  to  the  open  air.  The  purpose 
of  the  pot  or  chamber  is  that  any  explosions  due  to  defective 
propagation  of  the  flame  in  the  mixture,  or  due  to  improperly 
timed  ignitions,  may  occur  in  the  pot  rather  than  at  a  place  where 
they  might  be  attended  with  more  danger  of  fire.  In  some  con- 
siderable plants  the  exhaust  from  the  engines  has  been  taken 
into  a  subterranean  cistern  fitted  with  a  loose  cover  of  planks 
and  weighted  with  iron.  The  purpose  of  this  structure  was  to 
form  a  relief -valve  for  the  harmless  release  of  explosion  energy 
which  escaped  from  the  cylinders  and  had  to  be  taken  care  of  in 
the  exhaust  circuit. 

155.  Back-pressure  of  Exhaust-gases.  —  In  the  ordinary 
Otto  cycle  the  gases  at  the  end  of  the  working  stroke  will  have 
a  pressure  of  varying  intensity,  but  considerably  above  that  of 
the  atmosphere.  This  fact  explains  a  considerable  noise  in  the 
escape  of  the  exhaust-gases,  since  they  are  at  pressures  and  tem- 
peratures above  that  of  the  atmosphere,  which  will  result  in  a 
considerable  release  of  energy  when  they  come  together.  The 
volume  of  the  exhaust-gases  will  be  increased  by  the  release  of 
the  pressure,  but  diminished  by  the  drop  in  temperature.  If  the 
pressure  be  nearly  that  of  the  atmosphere,  the  effect  of  the  tem- 
perature change  is  to  diminish  the  volume,  while  if  the  pressure" 
is  above  the  atmosphere,  the  tendency  to  expand  takes  prece- 
dence over  the  tendency  to  contract.  The  expansion  is  the  occa- 
sion of  the  noisy  cough  which  is  more  frequent  than  the  other 
effect. 

The  Clerk  system,  which  has  the  exhaust-port  uncovered  by 
the  traverse  of  the  piston  near  the  end  .of  its  stroke,  and  which  is 
used  in  most  of  the  two-phase  engines,  can  be  used  with  or  with- 
out an  additional  exhaust- valve.  When  used  with  a  second  valve, 
it  will  be  apparent  that  the  release  of  pressure  by  the  uncovering 
of  the  lateral  port  in  the  cylinder  takes  off  much  of  the  pres- 
sure against  which  the  lifting  poppet-valve  in  the  Otto  system 


294  THE   GAS-ENGINE. 

has  to  work.  Among  the  engines  using  this  double-exhaust  are 
the  White  and  Middleton,  the  New  Era,  and  the  Springfield 
machines.  The  Clerk  port,  being  without  effect  on  the  back- 
pressure of  the  return  or  exhaust  stroke,  can  have  its  pipe  and 
its  noise  very  effectively  muffled  (§  156),  while  the  low  pressure 
prevailing  during  the  cleansing  stroke  causes  little  noise  in  any 
case.  If  there  are  two  exhaust-ports,  it  is  convenient  to  pipe 
them  separately,  since  the  pressures  in  each  pipe  will  differ  widely 
as  will  also  the  phenomena  connected ^with  them. 

The  considerable  pressure  on  the  inner  or  pressure  side  of  the 
exhaust-valves  throws  a  considerable  strain  also  on  the  cams 
by  which  they  are  lifted,  particularly  in  large  engines  where  the 
valve  will  have  a  large  diameter  to  give  sufficient  area.  This 
strain  wears  the  cam  and  the  roller  and  pins,  and  tends  to  buckle 
the  valve- spindle  when  the  cam  is  in  the  plane  of  the  valve;  or 
when  operated  through  rock-shaft  and  arms,  the  latter  are  sub- 
jected to  torsion  and  flexure.  This  condition  has  led  to  the  use  of 
balanced  valves  of  the  double-seat  or  poppet  type,  and  to  the 
use  of  balancing  pistons,  so  that  the  pressure  of  the  expanded 
charge  on  the  area  of  the  valve  should  be  counterbalanced  to  a 
great  degree,  leaving  only  enough  excess  on  the  valve  to  hold 
it  firmly  to  its  seat,  and  leaving  only  to  the  cams  or  levers  the 
work  of  overcoming  weight,  friction,  and  this  small  unbalanced 
excess  of  pressure. 

156.  Muffling  of  the  Exhaust— In  order  to  diminish  the 
unpleasant  noise  resulting  from  the  pressure  and  change  of  volume 
of  the  exhaust  as  it  escapes  into  the  open  air,  a  number  of  devices 
have  been  presented  on  various  designs  of  machine,  which  are 
known  as  mufflers  in  America,  and  as  silencers  in  English  and 
European  practice.  The  theory  of  the  silencers  or  mufflers  is 
to  secure  one  or  all  of  four  results.  The  first  is  to  reduce  the 
pressure  of  the  gases  until  they  are  as  nearly  as  convenient  at 
the  same  pressure  as  the  atmosphere  when  they  are  ready  to  es- 
cape into  it.  Second,  this  is  secured  by  allowing  the  gases  to 
expand  in  volume  and  in  this  process  to  become  cool.  Third, 
the  effect  of  such  expansion,  which  is  the  manifestation  of  the 


THE  COMBUSTION-CHAMBER  AND   THE  EXHAUST. 


295 


j 


FIG.  90. 


reduction  of  pressure,  is  to  diminish  the  velocity  with  which  the 
gases  escape  into  the  open  air,  which  velocity  is  partly  the  occa- 
sion of  noise.  Fourth,  all  of  these 
foregoing  results  are  helped  if  the 
body  of  escaping  gas  is  broken 
into  a  number  of  smaller  streams, 
by  being  baffled  and  allowed  to 
escape  through  a  large  area  in 
divided  form.  Any  construction 
of  muffler  which  will  reach  these 
results  will  meet  the  case.  It  is 
quite  usual  to  use  a  piece  of  pipe 
or  tube  of  diameter  considerably 
greater  than  that  of  the  exhaust- 
pipe  (Fig.  90),  and  to  allow  the 
exhaust-gases  to  enter  into  that 
larger  pipe  or  tube  through  a 
number  of  small  openings  where- 
by the  volume  of  the  gas  is  gradually  increased,  its  pressure  re- 
duced, the  volume  expanded,  and  the  final  discharge  takes  place 
through  a  great  number  of  openings. 

Other  plans  are  to  fill  the  enlarged  pipe  or  tube  with  baffling 
partitions,  so  that  the  velocity  of  the  gas  is  greatly  retarded,  while 
the  areas  through  which  it  passes  are  large  enough  to  result  in  no 
back-pressure  upon  the  exhaust-pipe,  and  at  the  free  end  the 
velocity  is  very  low.  The  muffler  can  conveniently  be  at  some 
considerable  distance  from  the  engine  (Fig.  91),  so  that  in  the 
length  of  pipe  which  couples  the  engine  to  the  muffler,  there  may 
be  opportunity  for  the  cooling  of  the  gases  before  they  enter  the 
muffler.  If  this  cooling  can  occur,  it  is  followed  by  a  lowering 
of  the  pressure,  a  diminution  of  the  volume,  and  a  greater  effect 
of  the  muffler  in  silencing  the  noise  of  the  escape.  The  baffling 
in  the  muffler  can  be  done  with  perforated  plates,  with  coils  of 
wire,  with  pebbles  or  balls,  through  which  the  gases  must  pass 
on  their  way  out. 

Unless  this  baffling  device  is  located  in  chambers  of  enlarged 


296 


THE  GAS-ENGINE. 


volume,  it  will  be  apparent  that  the  tendency  of  this  plan  of  silen- 
cing will  be  to  produce  an  increased  back-pressure  on  the  exhaust 


p    - 


FIG.  91. 

stroke  of  the  cylinder.  This  may  be  enough  to  invade  the  powei 
of  the  stroke  by  acting  in  the  same  way  as  the  method  of  govern- 
ing by  throttling  the  exhaust.  In  many  forms  of  the  automo- 
bile engine  a  by-pass  is  arranged  so  that  when  the  motor  is  to 
propel  the  carriage  slowly,  as  in  city  streets,  the  muffler  will  be 
in  action  and  the  exhaust  silenced;  when  the  open  country  is 
reached,  where  noise  is  of  less  moment,  the  muffler  is  switched 
off  and  the  exhaust  takes  place  freely  through  a  direct  connection 
to  the  air,  with  the  attendant  noise,  but  diminished  back-pressure. 
To  be  effective,  a  muffler  should  be  of  large  volume. 

In  the  exhaust-pipes  from  stationary  motors,  discharging 
into  the  open  air,  an  effective  silencing  has  been  secured  by  the 
simple  expedient  of  cutting  slots  in  the  side  of  the  pipe  near  its 
end,  so  that  as  the  moving  column  of  gas  drew  near  to  the  open- 
ing, whereby  it  would  naturally  escape  with  considerable  velocity 
into  the  air,  the  pressure  was  allowed  to  fall  by  a  free  but  gradual 
expansion  through  these  slots  sidewise.  The  principle  of  this 
suggestion  is  undeniably  sound  in  the  light  of  the  foregoing  dis- 
cussion. 


CHAPTER  XV. 

MANIPULATION  OF  GAS-ENGINES. 

160.  Introductory.  —  The    gas-engine   appears   in   so   many 
forms  which  differ  in  detail  to  such  an  extent  that  it  is  not  easy 
to  give  suggestions  as  to  the  manipulation  of  such  machines  which 
shall  be  applicable  in  every  case,  or  which  shall  apply  to  all  forms 
of  the  internal-combustion  engine.      Certain  fundamental  prin- 
ciples, however,  must  be  observed  in  all  cases,  to  which  attention 
may  properly  be  directed. 

161.  Effects  of  Quality  or   Richness  of  the  Gas. — If  the  gas 
used  in  the  motor  comes  from  a  street  main,  it  is  usually  of  a 
certain  standard  quality  or  calorific  power  and  will  not  be  likely 
to  vary  at  different  seasons  of  the  year  or  on  different  days.     Where 
the  gas  comes  from  a  producer,  it  is  likely  to  vary  in  richness  with 
variations  in  the  operation  of  the  producer  itself  and  variations 
in  the  fuel  from  which  the  gas  is  distilled.     But  the  widest  varia- 
tions and  those  which  are  the  sources  of  the  greatest  trouble  occur 
as  the   result  of  varying  carburation  of  the  gas  in  automobile 
motors,  and  from  such  action  of  the  governor  as  will  vary  the 
percentage  of  hydrocarbon  in  the  volume  of  the  mixture  of  air 
and  fuel  which  enters  the  cylinder  in  any  stroke. 

If  the  engine  be  adjusted  to  a  normal  running,  with  a  cer- 
tain proportion  of  air  and  fuel  in  the  mixture,  the  mixture  may 
be  varied  either  by  impoverishing  it  below  this  normal  proportion 
or  by  enriching  i,t  above  the  normal  (§§  100,  137).  If  the  mixture 
is  impoverished,  the  effect  will  be  likely  to  manifest  itself  in  a 
reluctance  to  ignite.  A  failure  to  ignite  will  obviously  result  in  no 

297 


298  THE  GAS-ENGINE. 

impulse  or  working  stroke  at  the  normal  interval  of  such  impulse 
which  will  result  either  in  the  motor  working  irregularly,  or  per- 
haps in  explosions  in  the  exhaust-pipe,  or  both.  Too  poor  a  mix- 
ture will  be  the  consequence  of  defective  working  of  the  carburetor 
or  inadequate  opening  of  the  fuel  inlet-valve.  An  impoverished 
mixture  will  be  particularly  annoying  where  hot-tube  or  hot-sur- 
face ignitions  are  used,  since  the  compression  may  not  produce 
a  temperature  sufficient  for  the  ignition  to  be  properly  timed 
with  respect  to  the  working  stroke.  If,  on  the  other  hand,  the 
mixture  be  enriched  above  the  normal,  there  may  result  an  irregu- 
lar working  due  to  pre-ignition  of  the  charge,  particularly  with 
hot-tube  systems  of  ignition,  since  the  temperature  of  such  rich 
mixture  will  be  raised  to  the  ignition-point  before  the  full  com- 
pression stroke  is  completed.  This  will  make  the  engine  work 
irregularly  and  with  considerable  sacrifice  of  its  full  capacity. 
It  is  obvious  that  too  rich  a  mixture  is  wasteful  of  fuel,  since  more 
than  the  necessary  amount  is  supplied  at  each  stroke,  and  while 
the  power  of  the  working  stroke  is  increased,  the  engine  will  be 
noisy  and  will  operate  with  considerable  shock  and  jar.  In  view 
of  the  principle  of  the  compression  cycle  it  is  of  advantage,  so  far 
as  the  volume  of  the  cylinder  is  concerned  and  the  economy  of 
fuel,  to  compress  to  a  considerable  degree  before  the  charge  is 
ignited,  and  it  is  desirable  not  to  make  the  charge  so  rich  as  to 
make  it  difficult  to  secure  a  high  compression  without  danger  of 
pre-ignition.  Pre-ignition  in  starting  the  engine  is  particularly 
annoying,  since  under  these  circumstances  the  motor  will  start 
backwards. 

162.  The  Starting  of  the  Engine. — The  first  step  in  the  pro- 
cess of  starting  a  gas-  or  gasoline-engine  is  to  see  that  all  the  appli- 
ances for  lubrication  are  full  of  oil  and  in  working  order.  The 
modern  engine  is  universally  supplied  with  sight-feed  oil-cups 
on  the  stationary  bearings,  either  as  single  units  or  having  a  com- 
mon reservoir  of  oil  from  which  small  pipes  lead  to  the  various 
points  requiring  to  be  oiled.  The  advantages  of  the.  reservoir 
system  are  that  it  is  easy  to  stop  the  flow  from  all  cups  at  once 


MANIPULATION  OF  GAS-ENGINES.  299 

when  stopping,  and  equally  to  start  all  cups  when  the  motor  is 
ready  to  start.  After  the  flow  is  once  adjusted  as  each  bearing 
may  require,  it  should  not  need  subsequent  attention,  except  to 
see  that  the  pipes  are  not  clogged  by  a  gumming  process  nor 
from  impurities  in  the  oil. 

After  the  oil-cups  and  lubrication  have  been  attended  to,  the 
ignition  circuit  should  be  next  made  ready.  If  the  ignition  is  by 
the  flame  system,  the  open  burner  is  ignited  by  turning  on  the  gas 
and  lighting  it  at  the  outlet.  If  the  hot-tube  system  or  the  hot- 
chamber  system  is  used,  the  necessary  heat  in  tube  or  chamber 
is  to  be  secured  by  starting  the  pre-heating  lamp  or  burner.  This 
pre-heating  lamp  may  be  of  any  of  the  types  which  will  meet 
the  purpose  of  bringing  the  surface  to  the  required  temperature, 
and  the  necessary  time  must  be  allowed  before  the  engine  is  to 
make  its  first  stroke.  If  the  electric-ignition  systems  are  used, 
it  is  desirable  to  examine  the  electrical  connections  and  to  see 
whether  the  spark  passes  or  the  arc  is  formed,  so  that  if  ignition 
should  fail,  the  origin  of  the  difficulty  may  be  known  to  be  in 
some  other  element  than  in  the  electric  circuit.  A  brief  treat- 
ment will  be  given  in  a  later  article  of  this  chapter  concerning 
the  usual  troubles  of  electric  ignitions. 

The  next  step  is  to  make  the  engine  begin  its  cycle.  This 
has  to  be  done  by  some  mechanical  force  acting  upon  the  crank- 
shaft to  move  the  piston  in  the  cylinder  so  as  to  cause  it  to  draw 
in  the  charge  of  air  and  fuel  on  the  outgoing  stroke  and  com- 
press that  charge  on  the  return  stroke  and  cause  the  ignition  as 
the  piston  draws  near  to  and  passes  the  dead-centre.  In  small 
engines  this  rotation  of  the  shaft  is  done  by  hand,  the  engine  be- 
ing turned  over  by  its  own  fly-wheel,  in  stationary  practice.  In 
automobile  practice  the  motor  is  released  from  the  driven  mech- 
anism by  throwing  out  a  clutch,  and  the  motor-shaft  is  turned  by 
hand  by  means  of  a  crank.  In  engines  of  the  middle  size  it  is 
quite  usual  to  arrange  a  special  cam  on  the  valve-shaft  which 
will  release  a  certain  amount  of  the  pressure  of  the  compression 
stroke  which  might  be  sufficient  to  prevent  the  hand-starting 


3co  THE  GAS-ENGINE. 

process  from  having  sufficient  power  to  bring  the  engine  to  its 
inner  dead-centre  and  cause  the  first  ignition.  In  large  plants 
some  mechanical  appliance  has  to  be  furnished  to  give  sufficient 
power  to  produce  these  first  compressions  and  first  ignitions. 
This  may  be  (par.  164)  a  storage  of  compressed  air,  or  in  plants 
of  sufficient  magnitude  a  small  independent  auxiliary  motor  may 
be  used  to  start  with.  It  is  better  to  make  the  starting  turning 
of  the  engine  with  some  speed,  since  the  compression  and  igni- 
tion are  more  certain  by  this  plan  than  when  the  turning  is  more 
leisurely.  When  everything  is  normal  the  engine  should  start 
within  two  revolutions  of  the  starting  effort  on  the  crank-shaft. 

It  is  an  obvious  advantage  of  the  multi-cylinder  engine  that 
one  of  its  cylinders  will  reach  the  phase  of  compression  and  igni- 
tion very  shortly  after  the  crank  is  started.  If  the  pistons  are 
tight  and  the  electric  method  of  ignition  is  used,  with  a  button 
which  can  make  a  spark  in  all  four  cylinders  at  once,  of  a  four- 
cylinder  motor,  it  will  be  apparent  that  when  the  engine  was 
stopped,  one  of  the  cylinders  had  either  a  partly  compressed 
charge  in  it  or  one  which  was  just  ready  to  be  ignited.  The 
partly  compressed  charge  can  be  used  to  start  the  motor-shaft, 
or  by  pressing  the  button  and  making  the  electrical  connection 
the  unused  charge  can  be  ignited  and  the  motor  started.  This 
action  is  secured  by  arranging  to  have  the  electric  ignition  dis- 
connected or  retarded  just  before  the  motor  is  stopped.  Otherwise 
the  ignition  of  the  partially  compressed  charge  before  the  dead- 
centre  is  reached  will  start  the  motor  backwards.  If  the  opera- 
tion of  the  starting  revolution  of  the  crank-shaft  does  not  begin 
the  cycle  and  the  ignition  is  known  to  be  in  good  order,  the  diffi- 
culty is  either  due  to  defective  carburation,  to  improper  com- 
pression, to  a  failure  of  the  fuel-supply,  or  to  improper  action 
of  the  inlet- valves.  In  some  forms  of  motor  the  moving  parts 
may  give  difficulty,  but  as  a  rule  when  this  is  the  case  the  engine 
is  difficult  or  impossible  to  start  by  hand.  After  the  engine  has 
begun  its  cycle  the  cam  which  releases  the  compression  should 
be  thrown  out  in  engines  which  are  fitted  with  it,  and  the  machine 


MANIPULATION  OF  GAS-ENGINES.  301 

will  at  once  take  up  the  speed  for  which  the  governor  adjusts  it. 
In  starting  motor-carriage  engines  with  the'transmission  machinery 
out  of  gear,  the  clutch  can  be  thrown  in,  and  usually  with  the 
low-speed  adjustment  in  gear  the  carriage  starts  more  easily  for 
the  occupants  and  with  less  strain  upon  the  driving  mechanism. 
When  the  inertia  of  the  carriage  and  the  first  friction  of  starting 
have  been  overcome,  then  the  other  gears  can  be  successively 
thrown  in.  The  adjustment  for  speed  in  variable-speed  engines, 
such  as  motor-cars,  will  be  done  by  the  governor  methods  dis- 
cussed in  Chapter  XII.  In  stationary  gas-engine  practice,  where 
the  supply  of  gas  is  regulated  by  a  gas-valve,  this  can  be  ad- 
justed tot  the  condition  of  operation  after  the  engine  has  reached 
its  speed. 

If  the  water-jacket  cooling  system  is  used,  operated  by  a  pump 
driven  from  the  engine  itself,  it  will,  of  course,  go  into  action  with 
the  starting  of  the  motor-shaft.  If  the  water-cooling  is  done  by 
the  circulation  from  a  city  supply,  the  necessary  valves  are  opened 
and  the  flow  regulated  to  maintain  the  desired  temperature  of 
the  outflowing  water.  In  motor-car  practice  the  circulating 
water  is  allowed  to  go  as  hot  as  is  consistent  with  keeping  it  from 
vaporizing  as  steam.  In  stationary  practice  more  water  is  used 
and  it  is  kept  cooler. 

It  is  undesirable  in  any  case  in  starting  to  have  the  electrical 
adjustment  of  the  ignition  set  for  a  pre-ignition  before  the  crank 
reaches  its  dead-centre.  If  this  precaution  is  not  taken,  the 
motor  may  back-fire  or  pre-ignite,  starting  to  revolve  in  the  wrong 
direction,  and  the  operator  at  the  starting  crank  is  liable  to  injury 
and  the  clutch  or  pin  mechanism  may  be  broken  by  which  the 
starting  crank  is  released  from  the  motor-shaft. 

163.  The  Stopping  of  the  Engine.  —  In  stationary  practice 
where  the  design  permits,  it  is  desirable  to  store  compressed  air 
or  compressed  charge  in  an  auxiliary  tank  or  reservoir  before 
the  engine  is  stopped,  so  that  by  connecting  this  compressed  air 
or  mixture  with  the  motor- cylinder  it  can  be  used  to  start  the 
first  stroke  and  save  the  inconvenience  and  annoyance  of  hand 


302  THE  GAS-ENGINE. 

starting.  This  implies  that  before  the  engine  is  stopped  the 
necessary  amount  of  compressed  air  or  mixture  shall  be  stored 
in  the  reservoir  by  throwing  in  the  appliance  whereby  this  is 
brought  about  (par.  164).  In  the  smaller  engines  in  motor- 
cars this  detail  is  disregarded.  The  motor  will  stop  when  the 
valve  is  closed  by  which  the  supply  of  fuel  for  the  mixture  is 
brought  to  the  cylinder.  Then  the  ignition  apparatus  will  be 
disconnected  by  throwing  out  the  switch  in  the  electric  system, 
or  by  extinguishing  the  flame  of  the  hot  tube  or  flame  ignition 
systems.  In  automobile  practice,  the  ignition  apparatus  will 
usually  be  thrown  out  first,  allowing  the  aspirated  mixture  to 
scavenge  the  cylinders  by  the  motion  of  the  car  before  it  stops. 
The  oil-cups  are  then  shut  off  and  the  cold-water  circulation 
stopped. 

164.  Restarting  after  a  Stop. — When  the  mechanism  driven 
by  a  gas-engine  has  to  be  stopped  frequently  and  then  started 
after  a  short  interval,  it  is  by  far  the  most  convenient  plan  to  in- 
troduce a  clutch  between  the  motor-shaft  and  the  driven  resist- 
ance, so  that  the  latter  may  be  stopped  without  stopping  the  motor. 
This  solution,  for  example,  is  the  universal  one  in  automobile 
practice,  and  it  is  a  convenient  one  in  the  general  case  also,  since 
the  starting  of  the  motor  with  the  resistance  coupled  to  it  in  large 
units  might  be  so  difficult  as  to  be  almost  impossible.  But  when 
the  motor  itself  is  to  be  stopped  and  is  to  be  restarted  after  a  period 
of  rest  the  condition  is  very  different  from  that  of  the  steam-engine, 
where  the  piston  starts  by  simply  opening  a  valve  which  connects 
the  piston  area  with  a  reservoir  of  sufficient  pressure  to  overcome 
the  resistance  and  the  engine  begins  its  normal  march.  The 
condition  to  be  met  is  the  rotation  of  the  motor-shaft  by  a  proper 
force  through  such  an  angle  as  shall  draw  in  a  charge  of  fuel  and 
air;  shall  compress  that  mixture  by  a  return  stroke  of  the  piston, 
and  carry  the  crank  up  to  and  just  beyond  that  point  at  which 
ignition  of  the  charge  takes  place.  In  single-cylinder  engines 
this  will  usually  require  one  revolution  at  least;  in  multiple- 
cylinder  engines  a  partial  revolution  should  be  enough.  By 


MANIPULATION  OF  GAS-ENGINES.  303 

what  means  shall  this  starting  action  be  caused,  so  that  the  motor 
may  be  restarted? 

If  the  normal  compression  pressure  be  60  or  80  pounds  per 
square  inch,  it  will  be  apparent  that  only  a  few  inches  of  area 
of  piston  will  be  required  that  the  resistance  to  compression 
may  exceed  the  capacity  of  the  human  muscles  to  meet  and 
overcome  it.  Hence  the  meaning  and  necessity  of  relieving 
devices  or  cams,  whereby  with  even  moderate  cylinder  diam- 
eters the  exhaust-valves  may  be  opened  enough  to  relieve  this 
compression  resistance  when  starting  by  hand,  and  with  the 
resistance  thrown  out.  This  may  also  be  done  by  opening  pet- 
cocks  discharging  from  the  compression  space,  which  are  closed 
as  soon  as  the  engine  will  take  care  of  itself.  The  handle  in 
Fig.  32  which  connects  the  pipe  E  to  the  cylinder  below  A 
is  such  a  relieving-valve.  Obviously,  however,  this  release 
of  the  compression  makes  a  weak  stroke,  and  with  greatly 
diminished  forward  energy.  In  discussing  the  methods  of  start- 
ing internal-combustion  motors,  therefore,  the  list  must  begin 
with 

i.  Hand-starting  with  fly-wheel  or  independent  crank.  This 
must  be  limited  to  comparatively  small  cylinder  diameters,  and 
demands  compression-relieving  appliances.  Care  must  be  taken 
lest  injury  be  done  with  high-speed  motors  from  the  cylinder 
overtaking  the  human  agency  and  starting  the  working  stroke 
before  the  hand  or  foot  can  be  released  from  the  lever  which  it 
is  using  to  start  the  shaft.  In  automobiles  it  is  quite  usual  to 
make  the  starting-crank  connect  to  the  motor-shaft  by  a  jaw,  or 
clutch,  so  designed  that  when  the  hand-crank  drives,  surfaces 
normal  to  the  effort  shall  receive  this  action.  When  the  motor 
overtakes  the  hand-crank,  the  contact  surfaces  are  oblique  to 
the  effort,  and  tend  to  force  the  crank-hub  along  the  shaft,  and 
disconnect  the  clutch  surfaces.  Back-firing  or  pre-ignitions  and 
a  reverse  of  the  motor-shaft  are  both  annoying  and  dangerous 
in  hand- starting.  The  limitations  of  this  system  for  large  instal- 
lations, or  for  small  ones  which  are  to  be  used  by  non-muscular 


3°4  THE  GAS-ENGINE. 

operators,  as  in  automobiles  for  use  by  women  and  children,  have 
turned  attention  to  other  systems. 

2.  In  multi-cylinder  engines,  if  the  ignition  system  be  electric 
and  switched  off  before  the  previous  stop,  the  inertia  of  the  fly- 
wheel of  the  motor  will  have  one  or  two  of  the  cylinders  charged 
with  mixture  which  has  been  compressed  and  which  has  begun 
to  expand  unignited  in  what  would  have  been  the  working  stroke. 
If,  then,  with  the  spark  adjustment  retarded  past  the  dead-centre, 
the  switch  be  thrown  in,  that  mixture  will  be  ignited  and  will  turn 
the  engine  over.     If  the  spark  adjustment  were  before  the  dead- 
centre  position,  and  the  charges  were  fired,  the  motor  would  start 
backward  on  the  charge  in  process  of  compression,  but  not  com- 
pletely compressed.     This  postulates,  of  course,  that  the  pistons 
fit  tightly  enough  to  hold  the  charge  of  mixture,  and  that  the  stop 
is  not  so  long  that  even  with  tight  pistons  all  compression  shall 
have  leaked  away.     This  system  is  available  only  in  the  electric 
systems  of  ignition,  but  its  possibility  is  an  additional  argument 
for  that  system. 

3.  A  storage  of  mechanical  energy  which  shall  be  potential 
or  available  in  quantity  to  start  the  motor.     The  simplest  system 
of  this  group  is  a  storage  of  compressed  air  in  air-tight  tanks.     In 
the  Westinghouse   system,  for   example   (par.   72),  an    air-com- 
pressor or  pump  is  thrown  into  gear  before  the  engine  stops  for 
a  period  sufficient  to  fill  the  necessary  tankage  with  air  at  150-200 
pounds  pressure.     When  the  engine  is  to  be  started,  one  of  the 
cylinders  is  by-passed  as  respects  the  gas-suction,  but  is  operated 
as  a  compressed-air  engine  using  air  from  the  storage  tanks. 

Assuming  that  the  cylinder  shown  in  Fig.  35  is  to  be  used  in 
this  way,  the  action  is  as  follows:  By  turning  a  screw  on  the  enc! 
of  the  upper  cam-shaft,  the  cam  B  is  thrown  out  of  action,  so  that 
the  admission-valve  /  remains  closed.  By  .moving  the  lever  seen 
on  the  outside  of  the  crank-case  near  the  cam  A,  this  cam  is  con- 
verted into  a  double-acting  one,  such  that  the  exhaust-valve  E  is 
open  on  every  up  stroke  of  the  piston.  Another  cam  on  the  same 
shaft  A  operates  a  valve  in  the  compressed-air  pipe,  permitting 


MANIPULATION  OF  GAS-ENGINES.  305 

compressed  air  to  enter  on  every  down  stroke  of  the  piston.  If 
now  the  crank  be  placed  in  the  proper  position,  and  the  air  turned 
on,  the  cylinder  will  operate  as  a  single-acting  compressed-air 
engine.  In  this  way  momentum  enough  is  secured  to  compress- 
a  charge  lightly  in  one  of  the  remaining  cylinders,  which,  on 
ignition,  augments  the  speed,  so  that  the  air-cylinder  may  be 
thrown  into  its  normal  working  condition.  A  very  simple  stop 
throws  the  compressed-air  valve  out  of  action,  and  a  motion  of 
the  lever  changes  the  exhaust-cam  to  its  original  condition.  By 
holding  a  knurled  head  at  the  end  of  the  upper  shaft,  the  rotation 
of  the  shaft  locks  the  admission-valve  cam  in  its  usual  position 
so  that  the  cylinder  operates  again  as  a  gas-engine. 

4.  The  fourth  system  of  the  same  general  class  compresses 
and  stores  an  explosive  mixture  of  gas  and  air  into  a  tight  reservoir. 
As  carried  out  in  the  Clerk  system,  with  an  independent  cylinder 
(Fig.  32)  for  the  aspiration  and  compressing  phases,  this  is  done 
by  a  by-pass  valve  between  the  motor  and  compressor  cylinder, 
so  that  an  occasional  cylinderful  from  the  compressing  phase 
is  delivered  to  the  reservoir  instead  of  to  the  combustion-chamber. 
Th's  can  be  done  at  intervals  just  before  shutting  down  the  motor 
without  seriously  affecting  it,  and  until  the  compression  pressure 
is  reached  in  the  reservoir.     When  the  motor  is  to  be  restarted 
after  a  stop  it  is  barred  over  into  a  crank-angle  just  past  the  dead- 
centre;    a  charge  from  the  pressure-reservoir  is  admitted  to  the 
combustion-chamber  behind  the  piston  through  a  pipe  and  valve ; 
the  mixture  is  fired  by  electric  spark,  and  the  march  of  the  engine 
begins. 

5.  A  variation  of  this  plan  is  to  have  an  auxiliary  hand -pump 
to  compress  mixture  into  the  space  behind  the  piston,  just  past 
its  dead-centre.     This  compressed  mixture  is  then  fired  either 
electrically  or  by  working  a  timing- valve  by  hand. 

6.  The  sixth  system  is  that  providing  an  auxiliary  or  external 
exploding-chamber  within  which  without  compression  an  explo- 
sive mixture  of  gas  and  air  may  be  gathered  and  ignited.     The 
pressure  from  the  expansion  caused  by  ignition  and  explosion 


3c6 


THE  GAS-ENGINE. 


passes  through  the  large  passage  at  the  top  of  Fig.  92  and  enters 
the  working  cylinder  through  the  inlet- valve,  and  has  force  enough 
to  start  the  engine  turning.  The  explosion  is  effected  by  a  pilot  - 
light  G.  As  long  as  gas  is  flowing  into  D  through  C  and  out  at  G 
me  flame  at  G  cannot  run  back.  When  C  is  closed  after  the 


FIG.  92. 

mixture  in  D  has  become  explosive  the  flame  runs  back  past  F 
and  fires  the  entire  charge. 

7.  Instead  of  one  explosion  being  used  to  start  me  working 
piston,  the  English  designers  have  used  a  succession  of  smaller 
explosions,  coming  after  each  other  and  acting  with  cumulative 
effect. 

8.  Belonging  also  to  this  group  is  the  proposed  plan  of  start- 
ing by  means  of  a  cartridge,  introduced  in  a  tube  into  the  cylinder 
from  without  and  detonated;    and  the  plan  of  igniting  the  first 


MANIPULATION  OF  GAS-ENGINES.  3° 7 

mixture  by  a  match,  firing  by  percussion  inside  the  cylinder. 
Here,  of  course,  the  charge  was  not  initially  compressed. 

9.  In  large  plants  an  auxiliary  or  "barring"  engine  inde- 
pendently driven  from  another  source  of  power  can  be  made  a 
starting  feature.  A  small  gas-engine  of  size  to  be  hand-started 
will  have  power  enough  when  started  to  put  the  massive  machine 
to  turning  over.  Or  the  auxiliary  may  be  a  small  steam-engine 
or  electric  motor. 

165.  The  Lubrication  of  the  Engine. — The  heat  incident 
to  the  ignition  of  the  charge  in  the  gas-engine  cylinder  makes 
the  problem  of  its  lubrication  more  difficult  than  that  of  the  steam- 
engine.  If  an  animal  oil  is  used,  or,  worse,  a  vegetable  oil,  or  a 
lubricant  which  is  adulterated  with  either,  a  process  of  oxidation 
takes  place  whereby  the  oil  burns  to  a  hard  gum  which  adheres 
closely  to  the  surfaces  which  it  is  supposed  to  lubricate.  For 
these  reasons  the  mineral  oils  are  the  only  proper  ones,  and  these 
should  be  of  good  quality,  so  that  the  gumming  may  not  occur. 
With  the  mineral  oils,  on  the  other  hand,  a  difficulty  is  some- 
times met  that  the  oil  in  combination  with  heat  and  compression 
will  form  a  gas  which  will  pre-ignite  on  the  compression  stroke, 
giving  a  back-fire  and  a  tendency  for  the  engine  to  reverse.  The 
cylinder  cannot  be  lubricated  by  the  ordinary  methods  used  for 
steam-cylinders,  but  the  oil  has  to  be  pumped  in  either  by  pumps 
mechanically  operated  or  by  utilizing  the  varying  pressure  on 
the  oil  acting  through  suitably  arranged  check-valves.  Hori- 
zontal engines  are  usually  lubricated  as  to  the  cylinder  by  an  oil 
cup  which  supplies  the  front  or  cool  end  of  the  trunk  piston,  and 
the  movement  of  the  piston  over  this  lubricated  surface  of  the 
cool  end  of  the  cylinder  is  intended  to  secure  adequate  supply 
of  oil.  In  many  designs,  horizontal  or  vertical,  which  have  a 
closed  crank-pit  the  lubrication  of  the  piston  is  effected  by  a 
spattering  of  the  oil  from  the  oil-bath  in  which  the  crank  and 
connecting-rod-end  dip  at  each  revolution.  This  method  of  an 
oil-bath  in  the  crank-case  secures  the  lubrication  of  the  crank-pin 
and  main  shaft-bearing  also.  The  valves  of  nearly  all  engines 


308  THE  GAS-ENGINE. 

are  made  to  lift,  to  open,  inasmuch  as  it  would  be  difficult  to 
secure  a  lubrication  of  a  sliding  surface  under  the  conditions  of 
heat  to  which  these  valves  are  exposed.  This  difficulty  has  been 
the  occasion  of  abandoning  the  sliding  valve  of  the  early  designs. 
It  is,  furthermore,  impossible  to  lubricate  with  the  ordinary  oil 
any  surfaces  over  which  a  gasoline  vapor  can  have  access,  since 
the  latter  is  a  solvent  for  the  lubricating  oil  and  destroys  its 
properties  for  this  end.  If  the  cylinder  is  not  properly  cooled 
by  its  water-jacket,  the  oil  may  either  gasify  or  gum,  whereupon 
the  piston  growing  overheated  and  expanding  will  offer  excessive 
friction,  or  will  become  seized  in  the  bore  and  stop  the  engine. 
An  overexpanded  piston  usually  causes  a  thump  or  pound  in 
the  engine. 

For  the  external  bearings  any  accepted  form  of  lubricator 
or  system  of  lubrication  can  be  applied  which  will  give  a  con- 
tinuous supply  of  oil  as  needed. 

1 66.  Improper  Working  of  the  Engine.  The  Engine  Refuses 
to  Start  or  Work. — When  the  engine  refuses  to  start,  it  is 
usually  by  reason  of  defects  either  in  the  ignition,  mixture  pro- 
portion, the  carburation,  or  the  compression.  The  possible  igni- 
tion difficulties  will  be  different  according  to  the  system  of  igni- 
tion used  (Chapter  XI).  If  the  tube-ignition  is  used,  the  most 
usual  causes  of  failure  are  due  to  defects  in  the  platinum  or 
steel  tube  or  in  the  burner.  The  hot  tube  may  become  cracked, 
allowing  the  compressed  gas  to  escape,  or  the  tube  may  become 
coated  with  soot  on  the  inside.  The  joint  between  the  tube  and 
the  cylinder  may  also  leak.  The  leakage  from  the  joint  or  from 
the  tube  may  be  detected  with  a  match.  The  tube  may  be  cleansed 
by  gasoline  or  by  rubbing  out  the  tube  with  a  small  piece  of  emery- 
cloth  on  a  stick.  The  burners  which  heat  the  tube  are  usually 
of  the  Bunsen  class.  For  gasoline  the  upper  end  of  the  burner 
is  a  tube  in  which  is  inserted  a  small  plug  of  asbestos  in  a  sheath 
of  fine  brass  gauze.  The  upper  end  of  this  tube  has  a  nipple 
with  a  minute  hole  in  it,  and  the  gasoline  or  gas  will  escape  from 
this  small  orifice,  which  is  surrounded  by  a  larger  tube  acting 


MANIPULATION  OF  GAS-ENGINES.  309 

somewhat  like  a  cowl  and  forming  a  mixing-tube  for  the  fuel  and 
air  which  is  ignited  at  a  slit  in  the  top  of  the  cowl  or  mixing-tube. 
This  slit  is  directly  under  the  ignition-tube.  To  start  such  a 
gasoline  burner  a  little  cup  under  the  base  of  the  burner-tube 
receives  alcohol  by  which  the  tube  is  pre-heated  and  made  into 
a  vaporizer  for  the  gasoline.  Burners  of  this  class  not  infre- 
quently jump  and  put  themselves  out  when  first  started  and  im- 
properly heated.  The  burner  should  show  a  blue  flame.  If  it 
burns  yellow,  it  is  usually  by  reason  of  being  clogged,  although 
excessive  pressure  of  gasoline  from  the  source  of  supply  will  blow 
the  flame  out,  as  well  as  excessive  jolts  and  a  high  wind  in  car- 
motors.  These  constitute  difficulties  with  this  system.  If  the 
charge  is  ignited  too  early,  the  flame  heating  the  tube  should 
be  moved  nearer  to  its  closed  end.  The  tube  should  be  at  a 
good  red  heat  for  starting. 

For  the  failure  of  the  electric  ignitions  the  difficulties  are  likely 
to  originate  either  in  the  battery,  in  the  circuit,  or  in  the  sparking- 
plug.  From  the  magneto  or  dynamo  ignitions  the  battery  diffi- 
culties are  eliminated,  but  the  others  remain.  Satisfactory  con- 
ditions of  the  battery  may  be  assured  by  any  of  the  ordinary  test 
instruments  which  will  indicate  whether  the  current  is  flowing 
between  the  terminals.  In  motor-carriage  work  imperfect  insula- 
tion is  a  very  usual  form  of  difficulty  with  the  ignition,  since  it 
is  liable  to  be  burned  from  contact  with  hot  exhaust-pipes  or  the 
metal  of  the  cylinder,  to  be  cut  or  chafed  from  the  motion  of 
the  vehicle,  and  to  have  the  connection  with  the  binding-posts  or 
other  terminals  become  loose  or  dirty.  The  coil  (pars.  128,  129) 
by  which  the  self-induction  is  increased  in  the  arc  system  or  the 
secondary  current  formed  in  the  jump-spark  system  are  likely 
to  break  down  from  failure  of  insulation  whereby  the  circuit 
passes  across  instead  of  around  the  coil.  The  vibrator  must 
be  in  good  order  or  else  the  current  will  fail  to  form  in  the  secondary 
circuit.  The  plug  across  which  the  spark  passes  is  liable  to  fail 
either  by  the  cracking  of  the  porcelain  tube  which  is  used  to  insu- 
late the  two  terminals  from  each  other,  or  the  points  may  become 


3Jo  THE  GAS-ENGINE. 

sooty,  or  a  deposit  of  oil  may  take  place  on  them.  In  either 
case  the  spark  will  fail  to  pass.  If  they  touch,  there  will  be  no 
spark,  or  if  they  are  too  far  apart,  the  spark  may  not  have  inten- 
sity enough  to  jump  the  gap.  With  dynamo  or  magneto  igni- 
tions they  have  the  same  difficulties  as  the  jump-spark  systems, 
with  the  added  difficulty  that  the  contacts  may  become  oxidized. 

If  the  ignition  is  in  good  order  and  properly  timed,  the  car- 
buration  may  be  unsatisfactory  for  one  of  several  reasons : 

(1)  Proportions  of  air  and  gas  badly  adjusted. 

(2)  Carburetor  flooded. 

(3)  Carburetor  insufficiently  supplied. 

(4)  Cold  weather  or  damp  weather. 

(5)  Gasoline  of  poor  quality. 

(6)  Gasoline-valve  closed  partly  or  entirely. 

The  most  usual  difficulty  from  improper  proportions  is  the 
consequence  of  the  mixture  being  too  weak  in  fuel.  This  will 
occur  with  a  governor  system  which  throttles  the  fuel-supply 
without  throttling  the  air,  or  by  a  leakage  of  air  in  excess  through 
a  defective  joint  in  the  suction  circuit,  or  by  the  presence  of  excess 
of  products  of  combustion  in  the  suction  charge  which  will  so 
impoverish  the  mixture  that  with  a  spark  of  a  given  intensity 
or  a  hot  tube  with  a  given  temperature  it  will  fail  to  light.  This 
difficulty  is  to  be  corrected,  experimentally,  by  varying  the  mix- 
ture to  see  whether  by  such  variation  it  shall  be  possible  to  cause 
the  motor  to  make  its  first  explosion. 

If  the  carburetor  is  either  supplied  with  gasoline  in  excess 
or  not  enough  flows  to  it,  the  ad  justing- valves  of  the  carburetor 
are  to  be  reset  to  make  the  mixture  right.  Too  rich  a  mix- 
ture will  give  trouble  by  pre-igniting  and  back-firing  on  the  com- 
pression stroke,  and  it  will  also  give  an  exhaust  with  an  offensive 
odor  due  to  the  presence  of  gasoline  partially  oxidized,  but  not 
completely  burned.  When  the  mixture  has  become  too  rich, 
the  gasoline  supply  should  be  cut  off  and  the  engine  revolved 
With  the  air-inlets  open  until  the  first  explosions  succeed.  The 


MANIPULATION  OF  GAS-ENGINES.  311 

carburetor  may  fail  to  supply  gasoline  enough  by  reason  of  the 
nipple  or  spraying-nozzle  being  stopped  up.  Of  course  the  valves 
supplying  the  carburetor  may  have  been  left  shut,  or  the  gaso- 
line tank  may  be  empty. 

In  cold  weather  the  cylinder  will  be  at  a  low  temperature 
and  the  carburetor  will  itself  be  cold.  It  has  been  observed 
that  the  spark  often  fails  to  ignite  the  cold  mixture,  while  after 
the  metal  of  the  engine  has  become  thoroughly  warm  no  diffi- 
culty is  encountered.  The  vapor  is  given  off  in  the  cold  car- 
buretor less  readily  than  when  it  is  warm.  This  difficulty  is  met,, 
of  course,  mainly  in  automobile  engines  which  are  operated  in 
the  open  air.  Artificial  heat  by  a  torch  or  lamp  is  the  most 
effective  cure  for  this  failure.  The  same  is  true  of  the  difficulty 
from  damp  air,  which,  carrying  a  proportion  of  moisture,  will 
act  to  cool  the  charge  on  the  suction  or  compression  stroke,  and 
may  keep  it  low  enough  in  temperature  not  to  ignite  with  the  energy 
in  either  spark  or  hot  tube. 

Gasoline  may  be  of  inferior  quality  when  it  has  been  allowed 
to  stand  for  some  time,  particularly  under  circumstances  favor- 
able to  its  slow  vaporization.  Such  gasoline  becomes  reluctant 
to  vaporize  by  the  absence  of  the  more  volatile  constituents.  The 
gasoline  may  be  stale  in  the  carburetor  or  in  the  tank.  Gaso- 
line sometimes  also  has  water  or  oil  mixed  with  it  which,  of 
course,  greatly  interferes  with  its  fuel  qualities. 

The  starting  of  the  machine  by  hand  may  have  been  done 
slowly,  so  that  the  passage  of  the  air  on  the  suction  stroke  was 
not  sufficiently  rapid  to  carry,  mechanically,  the  spray  of  gaso- 
line into  the  cylinder.  This  is,  of  course,  corrected  by  turning 
the  starting-crank  more  rapidly. 

If  it  is  the  compression  phase  of  the  cycle  which  is  at  fault, 
it  will  be  the  result  of  leaks  either  in  the  fit  of  the  piston  in  the 
cylinder,  or  at  joints.  The  valves,  also,  which  should  seat  tight 
under  the  compression  stroke,  may  be  corroded  or  coated  so  that 
they  permit  an  escape  of  the  compressed  mixture.  Improper 
working  of  the  compression  is  revealed  to  the  hand- starting  pro- 


3*2  THE  GAS-ENGINE. 

cess.  A  gumming  of  old  oil  in  the  cylinder  may  also  produce 
the  effect  of  resistance  to  compression,,  or  a  similar  gumming  or 
sticking  of  the  packing-rings  will  allow  the  compression  to  escape. 
This  makes  it  desirable  that  every  motor  cylinder  have  a  means 
of  injecting  a  little  gasoline,  kerosene,  or  other  solvent  to  cause 
this  oil  to  be  dissolved  as  the  piston  is  operated  by  hand.  The 
phenomena  of  pre-ignition  may  be  mistaken  for  those  of  exces- 
sive compression.  If  the  timing  arrangements  for  ignition  are 
set  forward,  so  as  to  occur  before  the  piston  reaches  the  dead- 
centre,  the  motor- shaft  will  receive  a  backward  impulse. 

A  motor  which  has  started  properly  and  has  been  working 
satisfactorily  for  some  time  may  fail  to  work  properly  and  will 
gradually  lose  its  power  and  speed  and  tend  to  come  to  rest.  This 
condition  may  result  from  one  of  several  causes,  or  several  in 
combination.  The  piston  may  seize  in  the  cylinder,  or  excessive 
friction  be  set  up  by  reason  of  overheating  of  the  cylinder.  The 
most  frequent  cause  of  this  difficulty  is  the  failure  of  the  water- 
cooling  system.  The  failure  may  be  caused  by  the  circulating 
pump  in  motors  in  which  the  circulation  is  caused  mechanically 
by  this  means;  the  water  may  have  been  evaporated  off,  leaving 
the  quantity  in  circulation  too  small  to  carry  away  the  heat  in 
the  cylinder;  by  a  clogging  of  the  pipes  by  solid  matter,  or  by  the 
formation  of  an  air-lock  or  steam-lock  in  the  circulation  at  some 
point  where  either  air  or  steam  may  gather  and  refuse  to  be  dis- 
lodged by  the  circulation.  A  thick  incrustation  or  deposit  of 
mineral  matter  from  the  circulating  water  may  take  place  upon 
the  hot  surfaces,  if  the  circulating  water  is  used  at  a  point 
at  which  such  mineral  constituents  in  the  water  will  be  deposited 
upon  the  hot  surfaces.  They  will  form  a  cake  there  which 
will  be  a  non-conducting  surface,  so  far  as  cooling  effect  is  con- 
cerned. 

Defective  lubrication  will  cause  excessive  friction  and  the 
same  phenomena  of  overheating  will  occur.  The  lubricant 
may  fail  to  reach  the  desired  point  from  clogging  of  the  pipes  or 
because  the  lubricator  has  been  allowed  to  get  empty.  Over- 


MANIPULATION  OF  GAS-ENGINES,  313 

heating  may  also  result,  but  less  frequently,  from  the  use  of  too 
rich  a  mixture  in  the  cylinder. 

The  float-feed  carburetors  not  infrequently  fail  at  work  by 
reason  of  the  bending  or  sticking  of  the  needle-valve  or  because 
the  float  has  become  punctured  and  liquid  gasoline  has  leaked 
inside  it  so  as  to  destroy  its  relation  of  weight  to  that  of  the  gaso- 
line on  which  it  is  supposed  to  float.  The  carburetor  also  is  liable 
to  starvation  from  dirt  stopping  up  the  small  orifice  through  which 
gasoline  passes.  Not  infrequently,  also,  the  vent-hole  in  a  gravity- 
fed  gasoline-tank  becomes  stopped  up  so  that  the  air  cannot  enter 
to  take  the  place  of  the  gasoline  which  the  engine  would  like  to 
withdraw. 

167.  Usual  Causes  of  Failure  to  Operate. — In  addition  to 
the  maladjustments  of  igniter  and  carburetor  referred  to  in  the 
preceding  section,  and  treated  more  fully  in  Chapters  IX,  X,  and 
XI,  the  internal-combustion  engine  is  liable  to  difficulties  which 
would  not  come  under  those  heads.  The  engine  is  liable  to  lose 
its  full  power,  and  possibly  to  slow  down  gradually  till  it  stops. 
The  complete  stoppage  is  usually  due  to  one  or  more  of  the  causes 
referred  in  the  previous  section.  A  loss  of  power  may  usually 
be  attributed  to  leakages  or  clogging. 

Leakages  are  most  troublesome  in  the  valves  and  piston- 
rings,  and  in  joints.  If  the  valves  either  of  inlet  or  exhaust  will 
not  close  tight,  compression  is  lessened,  and  the  charge  escapes 
through  these  leaks  when  fired  instead  of  driving  the  piston.  The 
valves  and  seats  are  liable  to  warping  and  cracking  from  heat, 
and  from  erosion.  The  valves  of  alcohol-motors  are  particularly 
exposed  to  a  corrosive  action  when  the  alcohol  is  decomposed 
on  incomplete  combustion  so  as  to  become  hot  acetic  acid  in  part. 
The  tendency  to  corrode  and  become  leaky  makes  it  impera- 
tive in  the  design  of  the  engine  that  both  valves  and  seats  should 
be  easily  accessible  for  removal.  Wear  of  the  cam  or  of  the  roller 
operating  the  valves,  and  lost  motion  in  joints,  or  bending  of  the 
levers  or  stems  which  operate  the  valves  will  produce  this  same 
loss  of  normal  power.  The  piston-rings  are  liable  to  wear,  but 


314  THE   GAS-ENGINE. 

if  they  have  become  gummed  in  their  grooves  from  an  oxida- 
tion of  the  oil,  so  that  they  do  not  expand  easily,  they  will  per- 
mit leakage  of  pressure  around  them  and  loss  of  power.  Leaky 
rings  are  detectable  -  by  a  sort  of  barking  noise  when  the  ear  is 
near  the  open  end  of  the  piston-trunk,  and  by  the  appearance 
of  smoky  air  at  the  same  point. 

The  inlet-passages  of  the  motor  are  usually  protected  at  the 
air-intake  by  a  gauze  screen  of  some  sort,  and  in  the  carburetor 
passage  is  also  likely  some  mixing  or  distributing  surface.  Both 
of  these  are  liable  to  become  clogged  with  dirt  or  dust  or  soot, 
when  of  course  the  power  of  the  motor  begins  to  fail.  In  car- 
buretors of  the  liquid-surface  type,  where  the  carburation  process 
gradually  cools  the  liquid  fuel  and  surrounding  metal,  it  may 
easily  happen  in  damp,  cool  weather  that  the  watery  part  of  the 
incoming  air  may  grow  cold  enough  to  freeze  into  anchor-ice, 
gradually  stopping  the  flow. 

A  leak  from  the  water-jacket  into  the  working  parts  of  the 
motor  may  lower  the  temperature  of  a  part  which  should  nor- 
mally be  hot.  This  of  course  causes  a  loss  of  power,  but  is,  as 
a  rule,  of  most  annoyance  in  making  the  engine  reluctant  to  start 
and  reach  the  first  high  temperature  required.  In  a  hot-tube- 
igniter  system  a  failure  to  have  the  tube  hot  enough  will  make 
the  engine  miss  firing  its  charges  occasionally. 

The  occasional  missing  of  the  proper  firing  of  a  charge  not 
only  reduces  the  power  of  the  motor,  but  is  usually  the  occasion 
of  annoying  exhaust  explosions.  Misfiring  is  probably  due  to 
improper  mixing  or  carburation  (Chapters  IX  and  X)  or  due 
to  improper  ignition  (Chapter  XI).  It  will  be  obvious  that  in 
gasoline-motors  a  poor  quality  of  gasoline  will  cause  both  kinds 
of  trouble,  particularly  unreliable  ignitions.  In  hot-tube  systems 
the  tube  may  not  be  hot  enough,  or  may  be  heated  at  a  point 
so  near  its  closed  end  that  with  the  compression  used  the  gases 
held  in  that  tube  are  not  compressed  enough  to  let  the  first 
mixture  reach  the  hot  part  and  be  ignited.  Or  the  tube  itself 
or  the  pipe  heating  it  may  be  clogged.  In  electric  ignitions  the 


MANIPULATION  OF  GAS-ENGINES.  315 

trouble  will  be  with  battery,  coil,  or  circuit,  as  above  treated. 
The  explosive  charge  not  ignited  will  pass  out  when  the  exhaust- 
valve  is  opened,  and  may  be  fired  in  the  pipe  or  passages,  where 
it  will  cause  a  detonating  noise. 

Back-firing  into  the  inlet  connections  will  result  from  a  de- 
layed combustion  in  the  cylinder  which  is  not  completed  by  the 
time  the  inlet-valves  open  for  the  next  stroke,  so  that  the  explo- 
sive mixture  in  the  inlet-passages  is  fired  from  the  cylinder  and 
through  the  opened  inlet  valve  back  to  the  source  of  the  fuel-sup- 
ply. Slow-burning  mixtures  are  due  either  to  too  little  or  too 
much  fuel.  An  excess  of  liquid  fuel  is  particularly  liable  to  cause 
this  trouble.  In  two-cycle  engines  where  the  cylinder  is  supplied 
from  the  slightly  compressed  charge  of  mixture  in  a  closed  crank- 
case  (§§  73,  90),  when  back-firing  occurs  the  motor  stops  until 
new  fresh  charges  can  be  introduced  into  the  crank-case  or  in 
front  of  the  piston  before  it  will  start  again. 

Finally,  of  course,  the  motor  may  lose  power  by  the  over- 
heating of  its  mechanical  bearings  at  shaft,  crank-pin,  or  cross- 
head,  causing  these  to  seize  and  begin  to  cut.  These  difficulties 
should  be  met  naturally  by  the  usual  remedies  common  to  any 
machine  and  familiar  to  all  skilled  operators. 

The  engine  may  thump  or  pound  from  lost  motion  at  r.ny 
of  its  joints  in  the  mechanism,  wrhich  should  of  course  be  inves- 
tigated and  located  and  the  cause  removed.  But  a  pre-ignition 
of  the  charge  produces  a  deep,  heavy  pound,  differing  from  the 
mechanical  pound,  and  similar  to  that  in  a  steam-engine  due 
to  excessive  lead.  It  is  to  be  corrected  by  properly  timing  the 
ignition.  (Chapter  XI.) 

1 68.  Concluding  Summary. — It  will  be  apparent  from  the 
foregoing  that  the  gas-engine  differs  from  the  steam-engine  and 
other  forms  of  motor  which  make  use  of  stored  energy,  for  each 
stroke  or  cycle  is  an  independent  event  and  is,  therefore,  liable 
to  interference  from  purely  instantaneous  causes.  In  the  steam- 
engine  or  compressed-air  engine,  for  example,  the  failure  to  work 
will  be  a  gradually  manifested  phenomenon,  while  in  the  gas-en- 


3*6  THE   G4S-ENGINE. 

gine  the  failure  to  work  may  be  effected  instantaneously  by  any 
one  of  a  number  of  different  causes.  This  indicates  the  neces- 
sity for  a  careful  attention  to  all  details  necessary  for  successful 
operation  before  the  engine  is  started,  and  that  when  it  is  stopped 
it  should  also  be  inspected  to  see  whether  any  defects  have  de- 
veloped during  the  run.  It  is  the  indifference  or  the  ignorance 
of  the  operator  concerning  the  action  of  the  elements  which  affect 
the  running  of  the  motor  which  has  given  rise  to  the  impression 
that  the  explosive  engine  is  tricky  and  uncertain.  This  has  been, 
doubtless,  aggravated  by  the  introduction  of  appliances  still  in 
an  experimental  stage,  but  as  more  experience  is  gathered  and 
these  appliances  become  reduced  to  standard  forms  and  pro- 
portions, the  uncertainties  of  this  class  will  disappear. 


CHAPTER  XVI. 

THE  PERFORMANCE  OF  GAS-ENGINES  BY  TEST. 

170.  Introductory.  —  All  motors  of  the  piston  class  have  two 
standards  of  performance.  The  first  may  be  called  the  indi- 
cated horse-power,  which  is  based  upon  the  general  formula  (par. 
40)  in  which 


In  this  the  factor  P  in  the  second  member  denotes  the 
observed  or  calculated  mean  pressure  in  the  cylinder  prevailing 
during  the  working  stroke;  A  is  the  area  of  the  cylinder  in 
square  inches;  L,  the  length  of  the  stroke  in  feet;  and  N,  the 
number  of  explosions  or  ignitions  which  occur  in  a  minute.  It 
will  be  apparent  that  for  a  two-phase  or  four-phase  single- 
cylinder  engine  the  explosions  are  not  as  frequent  as  the  num- 
ber of  revolutions.  In  engines  of  the  hit-or-miss  governor  system 
the  number  of  explosions  may  be  considerably  less  than  the  num- 
ber of  revolutions  when  the  engine  is  running  lightly  loaded. 

The  other  standard  for  the  capacity  of  the  engine  is  called 
the  brake  horse-power  and  is  the  actual  work  in  foot-pounds 
delivered  at  the  revolving  shaft  of  the  engine  as  measured  by  an 
apparatus  devised  to  determine  the  net  output  in  foot-pounds. 
This  brake  horse-power  takes  no  account  of  the  energy  delivered 
to  the  cylinder  on  the  explosion  stroke,  but  does  take  account  of 
the  energy  stored  in  the  fly-wheel  in  excess  on  that  stroke  and 
given  out  during  the  other  phases  of  the  piston  operation  to  over- 
come the  resistance.  It  averages  out  these  inequalities  and  gives  a 

317 


3*3  THE   GAS-ENGINE. 

mean  result  independent  of  the  variations  of  piston  effort.  This 
brake  horse-power  is  the  commercially  valuable  unit,  since  the 
resistance  to  be  overcome  is  the  factor  which  determines  the  size 
of  the  cylinder  required.  It  is  apparent  that  the  brake  horse- 
power will  usually  be  less  than  the  indicated  horse-power  even 
in  four-cylinder  engines  by  reason  of  the  losses  between  the  head 
of  the  piston  and  the  revolving  crank-shaft. 

The  brake  horse-power  can  be  determined  by  fitting  on  the 
engine-shaft  a  drum  or  pulley  which  can  be  surrounded  with  a 
flexible  band  which  shall  constitute  a  brake,  or  by  the  ordinary 
brake-blocks  which  can  be  pressed  against  the  face  of  the  pulley. 
If  the  power  is  large,  a  projecting  arm  from  the  brake-block  or 
from  the  band  resting  upon  a  scale  platform  permits  the  effort 
in  pounds  to  be  measured  which  the  friction  surface  is  exerting. 
(Fig.  93.)  That  effort  in  pounds,  if  the  surfaces  did  not  slip, 


FIG.  93. 

would  be  exerted  through  a  space  per  revolution  which  is  the 
circumference  of  the  circle  whose  radius  is  the  distance  from 
the  centre  of  the  shaft  to  the  point  which  exerts  the  pressure  on 
the  scale.  This  number  of  pounds  multiplied  by  the  computed 
number  of  feet  gives  the  brake  foot-pounds  per  minute. 

It  has  been  found  more  convenient  in  small  sizes  to  make 
use  of  the  device  called  a  rope  brake  on  the  fly-wheel  of  the  engine 
(Fig.  94).  The  fly-wheel  is  surrounded  by  a  rope  band  which 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


3*9 


may  have  several  plies  in  it,  kept  in  place  upon  the  wheel  by  blocks 
of  wood.  The  friction  of  the  rope  tends  to  lift  a  weight  or  to 
exert  a  pressure  upon  a  scale,  while  a  weight  or  spring  appliance 
maintains  the  necessary  tension  upon  the  rope  to  hold  it  to  the 
wheel  with  the  necessary  friction.  The  pounds  on  the  scale 


FIG.  94. 


(less  the  tension  effort  if  the  weight  or  spring  is  attached  to  a 
fixed  point)  gives  an  indication  in  pounds  as  before,  and  the 
space  per  minute  through  which  any  point  of  the  circumference 
of  the  fly-wheel  passes  is  the  feet  through  which  those  pounds  are 
exerted.  It  has  been  found  inconvenient  to  use  the  rope  brake 
when  the  speed  of  the  circumference  of  the  fly-wheel  exceeded 
a  rate  of  400  linear  feet  per  minute  per  horse-power  to  be  absorbed. 
For  example,  if  P  be  the  net  effort  downward  on  the  scale,  and 
/  the  length  of  the  lever-arm  with  which  this  pressure  is  exerted 
on  the  weighing-scale,  and  N  be  the  number  of  revolutions  per 
minute,  then 

T»TJID  '  PX2XXIXN 

B.H.P.  per  minute  =  —  • 

33,000 


320 


THE   GAS-ENGINE. 


171.  The  Indicator  for  Gas-engine  Testing. — The  appara- 
tus used  in  determining  the  indicated  horse-power  to  measure 
the  mean  pressure  is  the  apparatus  known  for  steam-engine  test- 
ing as  the  steam-engine  indicator.  The  gas-engine  indicator 
differs  only  from  the  steam  form  in  that  the  demand  upon  it  is 
particularly  severe,  due  to  the  sudden  way  in  which  the  pressure 
is  applied  at  the  instant  of  ignition.  The  high  pressure  and 


FIG.  95. 

temperature  of  the  charge  also  make  great  demands  upon  the 
indicator.  For  this  reason  it  is  convenient  to  use  a  piston  of 
smaller  area  in  the  indicator  than  is  usual  in  steam  practice,  with 
a  view  to  eliminating  the  inaccuracies  which  would  be  caused 
by  inertia  in  the  piston  and  attachments.  The  high  speed  of 
the  gas-engine  makes  it  desirable  also  that  the  indicator-drum 
should  be  of  small  diameter,  that  inertia  effects  in  the  length  of 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


321 


the  card  may  also  be  reduced  to  their  lowest  terms.     Fig.  95 
shows  a  successful  form  of  gas-engine  indicator. 

To  impart  motion  to  the  indicator-drum  when  the  latter  is 
of  small  diameter,  some  form  of  reducing  motion  is  necessary. 
The  forms  which  are  acceptable  in  steam-engine  practice  are 
not  serviceable  with  the  gas-engine,  and  the  cord  from  the  drum 
to  the  reducing  motion  should  be  as  short  as  possible.  The  re- 
ducing mechanism  should  be  positively  driven  in  both  directions. 
Forms  of  reducing  motion  which  have  been  found  convenient 
and  satisfactory  are  shown  in  Fig.  96.  The  device  in  either 


FIG.  96. 

form  receives  its  motion  from  the  shaft  of  the  engine  by  a  small 
crank,  and  the  two  forms  are  adapted  to  horizontal  and  ver- 
tical engines  respectively. 

The  piping  of  the  indicator  to  the  combustion-chamber  should 
be  very  short  and  direct,  so  that  no  loss  of  time  or  effect  may  fol- 
low in  communicating  the  change  of  pressure  in  the  cylinder 
to  the  piston  of  the  indicator. 

172.  The  Apparatus  for  a  Test. — Besides  the  indicator  and 
the  brake  equipment,  the  test  of  the  gas-engine  must  also  give 


322  THE   GAS-ENGINE. 

the  consumption  of  fuel  per  horse-power  per  hour  of  the  run.  With 
a  gas-engine  using  ready-made  gas,  the  requirement  is  simply 
for  a  calibrated  gas-meter  on  the  suction  connection  of  the  engine 
which  shall  read  closely  and  accurately  enough  to  give  reliable 
data  concerning-  the  cubic  feet  of  gas  consumed  during  the  period 
of  the  test.  In  gasoline  or  liquid-fuel  engines  the  same  informa- 
tion is  required  concerning  the  weight  or  volume  of  the  liquid 
fuel  used  by  the  engine  per  horse-power  per  hour,  and  this  can 
be  ascertained  by  drawing  the  supply  of  liquid  fuel  from  a  vessel 
mounted  upon  scales  for  direct  measurement  of  the  weight  used, 
or  by  drawing  the  fuel  from  a  calibrated  vessel  which  shall  read 
directly  the  consumption  by  volume. 

It  is  further  necessary  in  a  complete  test  that  the  weight  and 
temperature  of  the  cooling  water  circulated  in  the  jackets  may 
be  observed  so  that  the  amount  of  heat  carried  away  by  this  cool- 
ing water  may  be  subtracted  from  the  heat  furnished  to  the  engine 
in  its  working  charges.  This  supply  of  cooling  water  may  be 
measured  by  calibrated  meters,  or  it  can  pass  through  weighing- 
tanks  upon  scales  whereby  its  weight  can  be  observed  directly. 
The  temperatures  before  entry  and  after  leaving  are  measured 
by  thermometers. 

It  is  also  interesting  and  serviceable  to  measure  the  tempera- 
ture of  the  exhaust-gases  to  determine  the  quantity  of  heat  which 
escapes  by  this  channel.  The  following  method  of  making  this 
observation  has  appeared  to  be  a  distinct  improvement  upon  any 
of  its  predecessors. 

173.  Fernald  &  Lucke's  Apparatus  to  Observe  Exhaust 
Temperatures. —  The  exhausted  products  of  combustion  carry 
with  them  an  amount  of  energy  which  is  observably  present  in 
the  form  of  temperature,  but  which  is  also  present  in  the  form  of 
elastic  tension  which  cannot  be  observed.  The  problem  is,  there- 
fore, to  reduce  the  exhaust-gases  to  atmospheric  pressure  with- 
out losing  temperature  in  the  process  and  then  to  observe  the 
temperature  of  the  expanded  gases.  This  result  was  attained 
after  mrny  trials  and  the  rejection  of  uncertain  solutions  by  the 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


323 


device  illustrated  in  Fig.  97.  The  exhaust  from  the  engine  passes 
into  a  chamber  of  fire-brick  or  common  brick,  or  made  of  fire- 
clay as  shown  in  the  left-hand  half  of  the  cut.  It  enters  the  cham- 
ber through  a  throttling  device  shown  in  the  right-hand  half, 
which  consists  of  a  T  of  the  proper  size  with  a  plug  in  the  top  and 
a  nipple  and  cap  at  the  bottom.  The  plug  is  drilled  to  carry  a 
J-inch  bolt,  with  spring  and  nut  at  the  top;  the  bolt  at  the  bot- 
tom carries  a  flat  iron  disk  which  rests  against  the  perforated  bot- 


FIG.  97. 

torn  of  the  cap.  The  gases  enter  into  the  branch  of  the  tee,  and 
any  desired  resistance  to  their  entry  into  the  chamber  can  be 
secured  by  tightening  the  nut  and  spring,  but  no  wire-drawing 
occurs  as  would  occur  if  the  passage  were  throttled  by  a  fixed 
valve.  By  so  adjusting  the  nut  and  spring,  and  by  by-passing 
part  of  the  exhaust  if  necessary,  the  exhaust-gases  enter  the  brick 
chamber  so  as  to  leave  it  at  atmospheric  pressure.  This  is  done 
by  setting  up  the  bricks  dry  if  a  made-brick  chamber  is  used, 
or  by  surrounding  the  notched  bottom  of  a  flue-chamber,  as 


THE   GAS-ENGINE. 


shown  in  Fig.  97,  with  a  rubber  band  acting  as  a  flap- valve  to 
open  outward  and  release  any  pressure  within.  Thermometers 
giving  the  sensible  temperature,  without  effect  of  radiation  from 
the  walls,  may  be  read  for  the  actual  temperature  and  amount 
of  heat  energy  escaping  with  the  products  of  combustion.  Tc 
use  the  results  of  a  test  employing  this  apparatus,  the  first  com- 
putations involve  the  determination  of  the  combined  volumes  of 
air  and  gas  per  stroke  and  their  temperatures;  after  that  the 
temperature  of  the  final  mixture  in  the  cylinder  is  to  be  found. 
For  the  first  step,  assuming  the  temperatures  of  gas  and  air  to 
be  the  same,  the  data  and  computations  will  be  as  follows: 


=  air  per 


Solution. 


g 


Data  Given. 

Mins.  =No.  minutes  in  time  interval. 

item  19 

e.  =  gas  per  mm .  =  — ; . 

mins. 

_item  13 
mins. 

T2=  absolute  temp.  gas. 
Tl=  absolute  temp.  air. 

—  item  (21  or  15) +459°. 
Ex.  P.  M.  =  explosions  p.  min.  =  item  6. 
R.  P.  M.    —  revolutions  p.min.  =  item  4. 
Ms.  P.  M.  =  explosions  missed  per  min. 
=  \R.P.M.-Ex.  P.  M.  for 
single-cylinder  four-cycle 
engine. 

To  Find— 

2/  =  cu.  ft.  gas  per  explosion  at  7\.       I 
7/'  =  cu.  ft.  air  per  explosion  at  T2. 
Tag  =  absolute   temperature   in    F.°   re-  i 
suiting  from  combining  air  ar.d  j 
gas  at  Tt  and  T2. 

Vag=  combined   vol.    in    cu.    ft.    of   air 
and  gas  per  explosion  at  Tag. 


The  "  item  "  with  its  number  refers  to  the  scheme  of  a,  log 
record,  presented  hereafter  in  paragraph  174.  If  the  gas  and  air 
are  not  at  the  same  temperatures,  the  second  alternative  method 
to  find  the  same  data  is  as  follows: 


Ex.  P.  M. 
,,_  a-v'[Ms.P.M.] 

~[iR~P.  M.] 
Since      T,\g  =  (  T^  +  T2)  X  |,     [see  Note,] 


NOTE. — If  a  and^have  the  same  spec, 
heat  and  same  spec,  gravity.  If  not, 
then  work  out  on  the  basis  of  heat  lost 
by  one  equal  to  the  heat  gained  by  other. 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


32$ 


Data  Given.    - 

Mins.*=No.  minutes  in  time  interval. 
item  10 


mms. 


=  air  per  mm. 


Solution. 

The    general   equation   from   which 
Tag  can  be  computed  is 


It  is  now  necessary  to  find  Wa  and  wg 
If  it  is  not  convenient  to  obtain  the 
weight  of  gas  per  cubic  foot,  the  best 
that  can  be  done  is  to  take  the  weight 
of  gas  the  same  as  that  of  air  at  the 
same  temperature.  The  error  involved 
by  so  doing  is  not  serious. 

T 

Then  w,=wn— ; 


Tag  can  now  be  computed  from  the 
equation  above. 


; 


Vag    = 


T*!  =  absolute  temp,  air  in  F.°. 

=  item  15  +  459°. 
T2=  absolute  temp,  gas  in  F.°. 

=  item  21  +  459°. 
Ex.  P.  M.  =  explosions    per    minute  = 

item  6. 
R.  P.  M.    =  revolutions    per    minute  = 

item  4. 

Ms.  P.  M.  =  explosions  missed  per  min. 
=  %R.  P.  M.-Ex.  P.  M.  for 
single-cylinder  four-cycle 
engine. 

W!  =  wgt.  per  cu.  ft.  air  at  T\  =  item  16. 
W0=wgt.   per  cu.   ft.   air  at   32°   F.= 

.0807  Ib. 
T0  =  absolute    temp,    corresponding    to 

v'  =cu.  ft.  gas  per  explosion    j        as 

at  T2  [    found 

v"  =  cu.  ft.  air  per  explosion    |     under 

at  T\  J    Case  i. 

Cp  =  specific    heat   of   air   at    constant 

pressure. 

To  Find— 

w2   =wgt.  cu.  ft.  gas  at  T2. 
wa   =  wgt.  of  air  per  explosion  at  T\. 
Wg   =  wgt-  °f  gas  Per  explosion  at  T2. 
Tag  =  absolute  temp,  in  F.°  resulting 

from  combining  air  at  7\  and 

gas  at  TV 

v'"  =  cu.  ft.  gas  per  explosion  at  Tag. 
v"" =  cu.  ft.  air  per  explosion  at  Tag. 
Vag  =  combined  vol.  in  cu.  ft.  of  air  and 

gas  per  explosion  at  Tag. 

For  the  second  part  of  the  computation,  the  problem  is  from 
the  data  of  the  first  pari;  to  determine  the  temperature  of  the  final 
mixture  in  the  cylinder  after  the  air  and  gas  have  united  with 


326 


THE  G4S-ENGINE. 


the  exhaust-gases  in  the  clearance  space  —  unless  the  engine  is  of 
the  scavenging  type. 

It  is  to  be  noticed  that  if  the  governor  is  of  the  hit-or-miss 
type,  the  exhaust  stroke  following  a  miss  corresponds  to  a  scaven- 
ging stroke. 


Data  Giver.. 

Assume  the  weight  of  the  final  mix- 
ture equal  to  the  weight  of  air  at  the  same 
temperature.  Assume  the  specific  heats 
of  the  different  mixtures  the  same  as  for 


=  weight    cu.    ft. .  air   at    32' 
.0807  Ib. 


F. 


T0  =  absolute  temp,  corresponding  to 

Cp  =  specific  heat  air  at  constant  pres- 
sure. 

=  specific  heat  air  and  gas  at  con- 
stant pressure. 
=  specific    heat    final    mixture    at 

constant  pressure. 

Tag  —  absolute  temp,  of  air  and  gas 
entering  cylinder  as  computed 
in  Part  I. 

Vag  =  cu.  ft.  air  and  gas  at  Tag  as  com- 
puted in  Part  I. 
Te  —  absolute   temp,   exhaust-gases   at 

atmospheric  pressure. 
=  temp.  observed  and  recorded  in 

item  14  of  log+459°. 
vb    =  vol.  of  clearance  in  cu.  ft. 

To  Find— 
•wz=  weight  cu.  ft.  of  air  and  gas  at 

Tag. 

-a>4= weight    cu.    ft.    of   exhaust-gases 

atre. 

<Wag=  weight  of  air  and  gas  per  ex- 
plosion at  Tag. 

iut*=  weight  of  exhaust-gases  per  ex- 
plosion at  Te. 

3^=  absolute   temp,   of  final  mixture 

in  cylinder. 
Tm— 459°=  F.°  as  in  item  29. 


Solution, 


r^5 

Tag 


Tm  can  now  be  computed  from  the 
equation 

Cp(  Tm  -  Tag)Wag  =  Cp(  Te  - 
eW€ 


Wag  +  Wt 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST.  327 

Another  method  would  be  to  use  a  surface  condenser  with 
water-cooling  so  as  to  reduce  pressure  and  temperature  together. 
If  the  cooling  was  active  enough  the  gases  could  be  nearly  always 
brought  down  to  atmospheric  pressure  before  leaving  the  con- 
densing apparatus,  and  the  weight  and  temperature  range  of  the 
cooling  water  would  give  the  heat  energy  which  it  had  absorbed 
to  produce  this  result. 

It  may  or  may  not  be  desirable  according  to  the  desired  com- 
pleteness of  the  test,  to  make  observations  as  to  the  composition 
of  the  exhaust-gases.  A  full  and  complete  analysis  demands 
that  not  only  the  composition  of  the  inlet  gas  and  its  calorific 
power  be  made,  but  also  that  the  supply  of  inlet  air  be  measured 
as  well  as  the  composition  of  the  outgoing  products  of  combus- 
tion. 

174.  The  Observations  in  a  Test. — The  extent  and  num- 
ber of  the  observations  to  be  made  in  a  gas-engine  test  are  deter- 
mined by  the  results  which  are  sought.  If  the  object  is  simply 
to  determine  the  cubic  feet  of  gas  or  the  measure  of  liquid  fuel 
per  horse-power  per  hour,  a  preliminary  run  can  be  made  to 
determine  the  conditions  or  adjustments  which  give  greatest 
efficiency  and  to  make  sure  that  all  details  of  the  engine  are  per- 
forming their  functions,  as  well  as  possible.  The  engine  having 
been  put  in  its  most  favorable  condition,  the  test  is  then  begun 
with  the  observation  of  the  quantities  desired.  For  a  full  and 
exhaustive  investigation  to  determine  not  only  these  fundamental 
data,  but  also  questions  connected  with  the  utilization  of  the  heat 
and  the  quantity  of  heat  furnished  to  the  engine,  the  log  will  re- 
quire to  cover  a  very  much  wider  range  of  observations.  The 
accompanying  list  gives  a  full  series  of  headings  for  the  log  of 
such  test,  together  with  the  columns  for  the  computations.  It 
embodies  the  practice  found  serviceable  in  the  gas-engine  labora- 
tories of  Columbia  University,  where  its  form  originated. 

In  comment  and  explanation  as  to  the  accompanying  blank 
for  data  it  may  be  desirable  to  add  concerning  the  various  items 
the  following  computation-methods. 


328 


THE  GAS-ENGINE. 


. 

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THE  PERFORMANCE  OF  GAS-ENGINES  BY  TEST.  329 


•-' 


ffi    tc    ^ 


uotsuBdxa 


joj 


-spaBD-ao; 
Boipuj  luo 
sgaiissgaj 


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330 


THE  GAS-ENGINE. 


'BSJ^' 
£  S  £ 


« 


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^-     £ 
N"I  ikj 


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-saiouatoiyg 


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ggS 


THE  PERFORMANCE  OF  GAS-ENGINES  BY  TEST.  331 

No.  12.  Heat  in  the  Jackets. 

Since  the  specific  heat  of  water  is  taken  as  unity,  the  calcula- 
tion consists  only  in  multiplying  the  number  of  pounds  of  water 
used  during  the  interval  by  the  range  of  temperature,  this  range 
of  temperature  being  equal  to  the  number  of  heat-units  absorbed 
per  pound  of  water. 

Data  Given.  Solution. 

5  =  specific  heat  of  water  =  i. 
tr  =  temperature  range. 
W=  weight  water  for  time  interval. 

To  Find— 
hw=  B.T.U.  for  the  time  interval. 

No.  13.  Cubic  Feet.     No.  14.  Cubic  Feet  per  Hour. 

In  reading  the  ordinary  meter  it  is  not  sufficiently  accurate 
to  catch  the  readings  by  noting  the  positions  of  the  index  hands 
at  the  beginning  and  close  of  the  time  interval,  but  it  is  necessary 
to  keep  an  observer  at  the  meter  and  require  the  readings  to  be 
taken  from  the  hand  which  indicates  the  single  cubic  feet,  and 
whose  complete  revolution  records  10  cubic  feet. 

The  cubic  feet  per  hour  are  readily  calculated  from  the  data 
for  the  given  time  interval. 

No.  1 6.  Weight  per  Cubic  Foot 

This  weight  is  that  of  a  cubic  foot  of  air  at  the  temperature 
given  in  item  15,  and  is  found  as  follows: 


Data  Given. 

weight   cubic    foot   air   at   32    de- 
grees Fahr.=  .0807  pound. 
32°+ 459°  =  491°  (absolute), 
absolute  temperature  of  air. 
item  15  +  459°. 

To  Find— 
wgt.  per  cu.  ft.  at  given  temp. 


Solution. 


'.0807^. 


No.  25.  Cubic  jeet  of  Standard  Gas  per  Hour,  at  60°  Fahr. 
and  at  14.7  Ibs.  pressure. 


332 


THE  GAS-ENGINE. 


Vg 
Tg 
pg 


Data  Given. 
=  cu.  ft.  of  gas  per  hour  at  tg°  F. 


absolute  temp,  of        =         4 
=  pressure  under  which  gas  is 

ing. 
=  14.7     lbs.  +  pressure     shown     by 

manometer. 
=  6o0+4590-5i90       F., 

temp,  of  standard  gas. 
=  atmospheric  pressure. 
=  14.7  Ibs.  per  square  inch. 

To  Find  — 
=  cu.  ft.  standard  gas  per  hour. 


flow- 


absolute 


Solution. 


Vg 


No.  28.  The  values  of  the  coefficient  n  are  to  be  computed 
carefully  from  the  data  and  formulae  discussed  in  paragraph  56. 

No.  29  has  been  referred  to  separately  in  the  previous  para- 
graph (173). 


FIG.  98. 


No.  32  is  the  length  of  the  line  LB  in  Fig.  98. 

No.  33  only  requires  care  in  case  these  are  explosion  waves 
as  in  Fig.  98.  By  marking  the  centre  points  of  these  waves,  and 
continuing  the  curve  of  the  expansion  line  through  some  lower 
point  and  these  centre  points,  a  fairly  accurate  determination 
can  be  made. 


THE  PERFORMANCE   OF  GAS-ENGINES  BY   TEST. 


333 


No.  34.  The  pressure  at  end  of  expansion  is  usually  the  point 
of  inflection  at  D.  The  pressure,  of  course,  is  measured  in  this 
and  in  No.  33  from  the  line  of  zero  pressure. 

No.  35.  Pressure  if  Expansion  were  Carried  to  End  of  Stroke. 

This  value  is  readily  obtained  from  the  equation  of  the  ex- 
pansion curve,  the  value  of  the  exponent  n  having  been  computed 
in  28.  If  the  expansion  were  thus  continued  it  would  give  the 
point  H,  as  shown  in  Fig.  98.  The  pressure  corresponding  to  the 
point  H  is  deduced  as  follows : 


Data  Given. 


Vl  =  volume  at  some  point  of  the  card. 
Pj  =  pressure  corresponding  to  V1. 
n  =  value  deduced  in  28. 
V-)  =  total  volume  of  cylinder. 


To  Find — 

P2  =  pressure  corresponding  to  V2 ',  i.e., 
if  expansion  continued  to  H. 


Solution. 


PT7  »_ 
"       — 


The  volumes  being  used  as  a  ratio, 
the  piston  area  may  be  omitted,  the  ratio 
of  lengths  being  the  same  as  the  ratio 
of  volumes,  as  is  customary  in  working 
with  indicator-cards. 


No.  36.  Mean  Effective  Pressure. 

The  area  of  the  diagram  in  Fig.  98  should  be  measured  by 
the  planimeter,  using  the  lengths  between  the  perpendiculars 
LM  and  RW,  or  LR.  Then  the  area  in  square  inches  divided 
by  the  length  of  the  diagram  in  inches,  multiplied  by  the  scale 
of  the  spring  used,  will  give  the  mean  effective  pressure  in  pounds 
per  square  inch. 


Data  Given. 

A  =  area  diagram,  sq.  ins. 
L  =  length  diagram,  ins. 
5= scale  of  spring  used. 

To  Find — 
A/.£.P.  =  mean  effective  pressure. 


Solution. 


THE  GAS-ENGINE. 


No.  37.  The  difficulties  of  exhaust-gas  measurement  have 
been  referred  to  in  paragraph  173  and  the  apparatus  convenient 
for  the  test.  The  computations  refer  to  Fig.  98  and  involve : 


Solution. 
The  volumes  at  A  and  H  being  equal, 


pa 


Data  Given. 
(See  Fig.  96.) 

Pa  =  pressure    at    A  =  atmosph.    pres- 
sure =  14.7  Ibs. 

ph=  pressure  at  H  =  value  of  item  35. 
Tm  =  absolute  temp,  of  mixture  at  at- 
mosph. pres.  =  item  29  +  459°. 

To  Find— 
Th  =  absolute  temp,  of  exhaust. 


No.  39.  Specific  heat  Cv  for  exhaust-gases  may  be  taken  the 
same  as  for  air  Cv  =  .i6gi  unless  it  is  convenient  to  measure  it 
directly. 

No.  40.  Air  to  Gas  to  Neutrals. 

By  "  neutrals  "  is  meant  the  products  of  combustion  left  in 
the  cylinder  of  a  non- scavenging  engine  after  exhaust— an  amount 
equal  in  volume  to  that  of  the  clearance  space. 

In  determining  the  proportions  called  for,  the  number  of  cubic 
feet  of  gas  is  taken  as  unity,  and  the  temperature  of  gas  is  taken 
as  the  basis  for  the  computation.  The  quantities  of  air  and 
neutrals  must  be  reduced  to  corresponding  amounts  at  this  tem- 
perature. 

The  cubic  feet  of  air  used  in  ten  minutes  or  an  hour  cannot 
be  taken  as  a  basis  of  comparison,  without  modification,  owing  to 
the  misses  of  explosions,  in  which  case  air  is  taken  into  the  cylinder 
without  gas. 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


335 


T2 
Te 


Data  Given. 
absolute     temperature     of     air= 

item  15  +  459°. 
absolute     temperature     of     gas  = 

item  21  +  459°. 

absolute    temp,    of    exhaust-gases 
=  item  14  of  log  +  459°. 

at  atmospheric  pressure. 
t/  =  cu.  ft.  gas  per  explosion  at  T2  as 

computed  in  29. 
v"  =  cu.  ft.  air  per  explosion  at  T1  as 

computed  in  29. 

ve  =  cu.  ft.  neutrals  per  explosion. 
=  volume  of  clearance  =  Vb. 

To  Find  — 

vx  =  cu.  ft.  air  per  explosion  at  T2. 
vz  =  cu.  ft.  neutrals  per  explosion  at  T2. 
vx:v':  vz=  ? 


Solution. 


/7"i  7"* 

J7  =  ^>      V*-V"^', 


Taking  vf  as  the  basis,  i.e.,  calling  it' 
unity,  then 

vx\vr \vt=*v"  -=?-:i:ve-z2-. 

J-  \  -ie 


No.  41.  Is  the  ratio  of  the  full  stroke  LR  in  Fig.  98  to  the 
length  from  the  perpendicular  LM  to  the  point  D  where  the  ex- 
haust opens. 

No.  42.  In  Fig.  98  vt  is  proportional  to  OL  and  v2  is  propor- 
tional to  OR ;  or 


v,      OL' 

No.  45.  Value  of  R. 

R  is  the  constant  which  enters  into  the   mathematical  state- 
ment of  the  law ;  PV  =  RT. 


Data  Given. 
P0=  atmospheric  pressure  per  sq.  ft. 

=  2117  Ibs.  per  sq.  ft 
v2  =  total  vol.  of  cylinder  in  cu.  ft. 
Tm  =  absolute  temperature  of  mixture 
filling  cylinder  before  compres- 
sion begins. 
=  item  29  +  459°. 

To  Find — 
R  —  a  constant. 


Solution. 
By  the  above  law: 


Tm 


336 


THE  GAS-ENGINE. 


No.  46.  Temperature,  Degrees  Fahr.,  at  Compression. 

Having  determined  R,  as  in  45,  the  temperatures  corre- 
sponding to  any  point  in  the  diagram  are  readily  determined  by 
the  general  formula  used  in  obtaining  R  after  solving  for  T. 


Data  Given. 
Ip  general, 

P  =  pressure  in  Ibs.  per  sq.  ft. 
V=  corresponding  volume  in  cu.  ft. 
R  =  constant  determined  in  45. 

To  Find — 

T=  absolute  temperature  corresponding 
to  the  point  of  the  diagram  se- 
lected for  the  temperatures  of 
compression. 


Solution. 

T-PV- 
~~~> 


No.  47.  Maximum  Temperature,  Degrees  Fahr. 

The  formula  in  No.  46  will  be  used  in  general,  and  if  the  igni- 
tion line  rises  vertically  from  the  point  of  maximum  compression, 
and  the  expansion  curve  drops  at  once  from-  the  maximum  pres- 
sure, the  computation  can  take  the  following  form: 


Data  Given. 
pc  =  maximum    pressure,    Ibs.    per   sq. 

in.  =  item  36. 
pb  =  compression  pressure,  Ibs.  per  sq. 

in.  =  item  35. 
jTi>=  absolute     temp,     at     compression 

=  item  46 +  459°. 

To  Find— 
Tc=  absolute  maximum  temperature. 


Solution. 


If  it  is  not  apparent  just  where  the  maximum  product  of  pres- 
sure into  corresponding  volume  did  actually  occur,  the  explo- 
sion end  of  the  diagram  may  be  divided  by  vertical  lines'  at  several 
points  on  the  line  of  that  part  of  the  stroke,  and  the  volume  being 
measured  and  the  pressure  scaled  off,  the  maximum  product  may 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


337 


be  those  found  experimentally,  and  these  values  used  for  P  and 
V  as  in  No.  46,  when  R  is  known  from  45. 
No.  51.  B.T.U.  Equivalent  to  Brake  H.-P. 


Data  Given. 

i  H.-P.  =  33,000  ft.-lbs.  per  min. 
i  B.T.U.  =  778  ft.-lbs. 

B.H.-P.  =  brake  horse-power  of  50. 
int.  =  time  interval  of  item  2. 

To  Find— 
B.T.U.  per  int.  equivalent  to  B.H.-P. 


Solution. 
B.T.U.  per  min.  for 


B.T.U.  per 

int.  =  42.4XB.H.-P.Xint 


No.   54.    Gas  H.-P.      No.   55.    B.T.U.  Equivalent   to  Gas 
H.-P.^H,. 


Data  Given. 

Ff/  =  heat  of  combustion  of  fuel  deter- 
mined by  analysis  or  calorimeter. 

.F=lbs.  of  coal  or  oil,  or  cu.  ft.  of 
standard  gas  per  interval. 

To  Find— 

equivalent  to  G.H.-P . 


Solution. 


33,oooXint.' 

No.  56.   Heat  Supplied  B.T.U.  from  Indicator-card =H^. 

If  the  specific  heat  of  the  gases  be  assumed  to  be  the  same 
before  and  after  explosion,  and  assumed  to  be  the  same  as  for 
air,  the  computation  is  much  simplified  and  no  serious  error  in- 
troduced. 


338 


THE  G4S-ENGINE. 


Data  Given. 

Tm*=  absolute  temperature  of  mixture 
in  cylinder  before  compression 
=  item  49  +  459°. 

Tag=  absolute  temp,  of  entering  air 
and  gas  as  computed  in  para- 
graph 29. 

Vop=-vol.  of  entering  air  and  gas  per 
explosion  at  Tag  as  computed 
in  Part  I  of  29. 

Vb=  clearance  vol.  of  cylinder. 
w5  =  wgt.  per  cu.  ft.  of  mixture  at 

Tm  as  computed  in  30. 
Cv  =  specific  heat  at  constant  vol.= 

.1691. 
!TC=  absolute   temp,   of  point   C  of 

diagram. 
J5=  absolute  temp,  of   compression 

=  item  46  +  459°. 

Exps.  =  total    explosions  per    time    in- 
terval. 

To  Find — 

z^  =  vol.  entering  air  and  gas  at  Tm. 
v  =  total  vol.  per  explosion  of  mix- 
ture before  compressing. 
ivm  =  total  wgt.  of  mixture  in  cylinder, 
supplied    in    B.T.U.    per 
time  interval. 


Solution. 


Cv(  Tc~ 


No.  57.  Heat  Extracted,  B.T.U.,  by  Observation  =  H2. 

This  value  is  determined  by  an  analysis  of  the  exhaust-gases 
from  which  the  heat  equivalent  of  a  cubic  foot  of  these  gases  is 
determined. 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST. 


339 


Vag 
Tk 


Exps. 
w6 


Data  Given. 
absolute  temp,  exhaust  at  at- 

mospheric pressure. 
item  14  of  log  +  459°. 
absolute  temp,  of  entering  mix- 

ture =  item  29  +  459°- 
specific  heat  at  constant  pressure. 
absolute  temp,  of  combined  air 

and  gas  as  found  in  29. 
combined  vol.  of  air  and  gas  per 

explosion  at  Tag. 
absolute    temp,  of   exhaust   as 

analyzed. 
B.T.U.    per    cu.    ft.    exhaust 

gases    at    Tk    as    found    by 

analysis. 

explosions  per  time  interval. 
"weight  per  cu.  ft.  by  analysis. 


ToF:.ndr— 

•uk  =  vol.  in  cu.  ft.  at  Tk  per  explosion. 
•Wk  =  total  weight  per  explosion. 
H2=  total   heat   exhausted,  B.T.U., 
per  time  interval. 


Solution. 


NOTE. — If  the  exhaust-gases  are  in- 
combustible,  the  second  quantity  in 
brackets  becomes  zero. 


H2'. 


58.  Heat  Extracted,  B.T.U.,  from  Indicator-card 
This  is  the  heat  thrown  off  in  the  exhaust  as  derived  from 
the  pressures  shown  by  the  indicator-card. 

Solution. 


Data  Given. 
=  absolute  temp,  of  exhaust  =  item 

37  +  459°- 

=  absolute  temp,  of  mixture  at  at- 
mospheric  pressure  =  item  29  + 


459 


as  found  in  57. 


To  Find— 


HJ=IC(Th—Tn?). 


.H"/  =  heat  rejected,   B.T.U.,   per  time 
interval. 

The  elements  concerning  which  there  may  be  a  difference  of 
opinion  in  the  computations  will  be  principally  those  which  in- 
volve the  specific  heat  of  the  mixture  and  of  the  products  of  com- 
bustion. The  specific  heat  is  obviously  not  that  of  either  the 


340  THE  G4S-ENGINE. 

gas  by  itself  or  the  air  by  itself,  but  is  the  specific  heat  of  a  mechani- 
cal mixture.  This  actual  or  effective  specific  heat  (par.  55) 
is  a  quantity  which  will  affect  the  computations  of  the  diagram 
of  expansion  since  the  ratio  which  it  bears  to  the  specific  heat 
at  constant  volume  will  determine  the  exponent  to  be  used  in 
treating  the  expansion  according  to  the  adiabatic  law. 

175.  The  Precautions  against  Error  in  a  Test. — The  pre- 
cautions which  must  be  observed  in  conducting  a  gas-engine 
test  are  the  same  as  those  which  should  be  taken  in  conducting 
a  test  with  any  high-speed  engine  in  addition  to  certain  others 
which  are  the  consequence  of  the  peculiarities  of  the  engine 
itself.  In  the  first  place  the  spring  of  the  indicator  is  par- 
ticularly liable  to  error  from  the  heat  and  from  friction, 
and  the  inertia  effects  from  weight  of  the  parts,  and  par- 
ticularly from  the  paper  drum,  introduce  notable  errors  into  the 
indicator  diagram.  The  effects  upon  the  lines  of  the  diagram, 
due  to  defective  operation  of  the  igniter,  the  carburetor  and  the 
valves,  are  specially  liable  to  be  masked  by  defective  methods 
of  actuating  and  connecting  the  indicator.  Peculiarities  also  in 
the  behavior  of  the  phenomenon  of  propagation  of  the  flame  in 
the  mixture  are  liable  to  be  confounded  with  inertia  effects  and 
a  wrong  interpretation  is  very  easily  made.  Fig.  98,  which  bears 
all  the  appearance  of  a  diagram  suffering  from  inertia  of  the  indi- 
cator piston,  has  really  no  relation  to  such  inertia  but  solely  to 
the  presence  of  pockets  in  the  ignition  chamber  from  which  the 
propagation  of  energy  was  undulating.  (Paragraph  214.) 

In  tests  which  are  made  to  ascertain  the  satisfactory  work- 
ing of  the  engine,  great  care  must  be  taken  to  eliminate  the  effects 
of  other  causes  upon  those  which  are  being  particularly  studied. 
The  timing  of  the  ignition,  for  instance,  may  be  so  masked  by  a 
variation  in  the  rate  of  ignition  through  the  mass  as  to  make 
it  very  difficult  to  separate  accurately  the  effect  due  to  each  sepa- 
rate cause.  As  discussed  in  the  previous  chapter,  the  engine  is 
particularly  liable  to  defective  working  as  the  result  of  improper 
lubrication,  and  as  each  stroke  or  each  cycle  stands  by  itself, 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST.  34* 

and  independent  of  every  other,  the  forming  of  an  average  con- 
dition or  standard  is  more  difficult  than  in  the  case  of  the  steam- 
engine. 

It  must  be  observed,  furthermore,  that  if  the  governing  oper- 
ations are  in  action  during  the  test,  that  these  will  introduce  wide 
variations  from  the  conditions  which  are  found  best  for  one  par- 
ticular resistance  and  speed.  It  will  be  obvious  that  if  the  mix- 
ture is  varied  in  composition  a  number  of  attendant  and  coinci- 
dent changes  should  be  made  if  the  engine  is  to  be  equally  effi- 
cient under  these  changed  conditions  of  resistance.  These,  of 
course,  it  is  difficult  to  meet  so  that  a  test  is  only  fair  to  the  motor 
when  it  is  made  under  practically  constant  conditions,  so  far  as 
resistance  and  speed  are  concerned.  This  is  particularly  true 
so  far  as  liquid  fuel  engines  are  dependent  upon  the  effective 
action  of  their  carburetors  for  the  mixture  supplied  to  the  cylinder. 
Again,  variations  in  the  quality  of  the  fuel,  either  gaseous  or  liquid, 
supplied  to  the  engine  during  a  test  affect  that  part  of  the  test 
which  immediately  follows  such  change.  In  the  steam-engine, 
on  the  other  hand,  the  effect  of  any  such  changes  are  averaged 
up  into  the  run,  by  reason  of  the  storage  action  which  takes  place 
in  the  boiler  when  heat  from  the  fuel  is  stored  in  the  water. 

176.  The    Conclusions  from    a    Test. — The  list  of  columns 
in  a  complete  log  given  under  the  foregoing  paragraph  indicates 
the  conclusions  which  are  usually  required  and  deduced  from  the 
engine  test.     If  the  test  is  made  to  determine  the  economy  cr 
consumption  of  an  engine,  only  those  conclusions  are  drawn  from 
the  observations  which  are  required  for  the  purpose  in  hand.     It 
is  plainly  from  the   results  of  actual  tests,  completely  and  accu- 
rately made,  that  the  development  of  the  gas-engine  along  sound 
lines  is  to  be  looked  for. 

177.  Records    of   Performance    and   Economy. — It   is   diffi- 
cult to  present  records  of  tests  of  gas-  or  gasoline-engines  which 
shall  not  be  misleading  by  reason  of  a  lack  of  definite  statements 
concerning  all  the  elements  which  entered  into  the  test.     For 
instance,  the  quality  of  the  gas  as  to  calorific  power  and  source 


342 


THE  GAS-ENGINE. 


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THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST.  343 


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344  THE  GAS-ENGINE. 

is  often  omitted  from  the  record  and  only  the  cubic  feet  of  gas 
per  horse-power  given,  and  no  measure  taken  of  the  quality.  The 
character  of  kerosene  oil  used  in  various  tests  is  indicated  often 
merely  by  the  trade  name  and  with  kerosene  and  gasoline  the 
quality  is  often  a  variable  within  considerable  limits.  Stale 
gasoline  is,  of  course,  less  favorable  to  the  engine  than  fresh, 
but  a  difference  in  its  specific  gravity  will  make  a  considerable 
difference  in  the  quantity  required  to  do  a  given  work. 

The  most  reliable  tests  of  gas-engines  on  a  large  scale  have 
been  made  in  England  under  competitive  conditions  at  exhibi- 
tions and  in  the  table  which  precedes  several  of  these  competitive 
tests  are  reported.  The  American  records  of  tests  are  much  less 
complete  than  the  English.  In  the  case  of  the  gasoline-engine 
using  carbureted  air  it  is  particularly  important  to  compare  only 
engines  operated  under  somewhat  similar  conditions  as  to  speed 
and  fuel-supply.  The  effect  of  speed  in  varying  the  fuel  supply 
at  high  numbers  of  revolutions  introduces  an  important  variable 
in  such  records.  The  table  on  pages  284  and  285  presents  a 
series  of  the  data  which  have  been  taken  from  various  sources. 

178.  Sources  of  Loss  in  Actual  Engines  as  Compared  with 
the  Ideal. — By  an  examination  of  the  columns  headed  Heat  Dis- 
tribution, it  will  be  apparent  that  there  are  four  channels  through 
which  the  expenditure  of  the  heat  energy  occurs.  There  is,  first, 
the  mechanical  work  done  upon  the  piston  of  the  engine  and 
which  is  the  net  output  which  should  be  made  as  large  as  possible. 
It  will  be  noted  that  it  ranges  between  20  and  22  in  the  higher 
figures.  The  limitations  which  prevent  this  figure  from  reach- 
ing higher  values  are  set  by  the  necessity  for  keeping  the  metal 
of  the  cylinder  and  the  seats  of  the  valves  at  a  low  temperature, 
so  that  they  shall  not  undergo  too  rapid  deterioration  or  deform- 
ation from  the  high  heats  inside  the  cylinder,  and  so  that  it  shall 
be  possible  to  lubricate  the  surfaces  which  are  in  contact.  Re- 
cent experiments  have  shown  that  the  total  heat  distribution  is 
little  affected  by  changes  in  the  temperature  of  the  jacket-water 
between  40°  F.  and  the  boiling-point.  The  combined  withdrawal 


THE  PERFORMANCE  OF  GAS-ENGINES  BY   TEST.  345 

of  heat  by  the  two  sources  of  loss,  jacket- water  and  exhaust  tem- 
perature, ranges  between  70  and  80  per  cent.  The  balance,  which 
is  friction,  radiation,  leakage  and  the  like,  is  usually  a  small  per- 
centage and  ought  to  be  less  than  ten.  These  deductions  make 
it  evident  that  the  directions  open  for  the  most  manifest  improve- 
ment are  those  which  have  to  do  with  the  transformation  of  a 
greater  proportion  of  heat  into  mechanical  work  and  the  reduc- 
tion of  the  heat  which  in  the  present  forms  of  motor  has  to  be 
disposed  of  by  the  cylinder  either  through  the  jackets  or  at  the 
exhaust.  It  means  an  increase  in  the  temperature  range  in  the 
cylinder  without  securing  this  by  means  which  have  no  direct 
relation  to  the  mechanical  energy  utilized. 

The  most  obvious  of  the  methods  to  accomplish  this  purpose 
are  those  which  have  been  presented  by  Mr.  Atkinson.  His 
constructions  in  1885  and  1887  were  known  as  the  differential 
and  cycle  engines  and  were  designed  so  that  by  the  mechanism 
driving  of  the  crank  of  the  engine,  the  expansion  stroke  of  the 
piston  should  be  longer  in  travel  than  any  other  stroke  of  the  cycle. 
By  this  means  the  volumes  appropriate  to  compression  were 
expanded  after  ignition  to  a  volume  greater  before  the  exhaust 
opened  than  they  had  before  compression,  and  as  a  consequence 
the  terminal  pressure — and  therefore  also  the  mean  pressure — was 
lowered  while  the  external  work  was  being  done.  The  difficulty 
connected  with  both  designs  is  the  complication  of  mechanism 
which  has  to  be  introduced  in  order  to  bring  about  the  variable 
length  of  piston  traverse.  The  same  object  has  been  further 
sought  by  injecting  water  or  steam  into  the  mass  of  mixture  in 
the  expanding  cylinder,  with  the  idea  that  the  result  of  this  ac- 
tion would  be  to  compel  the  mixture  of  steam  and  air  to  partake 
more  nearly  of  the  expanding  action  of  steam  which,  in  expand- 
ing, parts  rapidly  with  its  heat,  while  the  permanent  gases,  like 
air,  are  reluctant  to  lower  their  temperature  by  expansion.  The 
difficulty  here  has  been  that  the  injection  of  the  steam  cooling 
the  mixture  lowers  the  mean  effective  pressure  and  diminishes 
the  net  driving  effort  of  the  piston. 


CHAPTER  XVII. 

THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 

180.  Introductory,,  —  In    the    foregoing    chapters    the    treat- 
ment of  the  internal  combustion  engine  has  been  mainly  from 
the  practical  or  experimental  point  of  view.     It  has  been  the  pur- 
pose to  point  out  the  operation  of  the  internal  combustion  motor 
working  under  the  usual  forms  in  which  the  theoretical  cycles 
have  been-  reduced  to  practice.     In  Chapter  IV  and  those  which 
preceded  it,  a  certain  amount  of  attention  was  given  to  the  cycle 
independent  of  the  motors  which  utilized  it  and  to  certain  theo- 
retical considerations  having  their  origin  and  deductive  treatment 
from  the  science  of  thermodynamics.     It  will  be  the  purpose 
of  the  present  chapter  to  treat  in  a  mathematical  way,  on  a  basis 
of  pure  theory,  the  cycles  which  are  available  for  use  with  the  in- 
ternal combustion  motor,  and  to  deduce  from  the  theoretical  equa- 
tions which  appear  in  such  analysis  some  serviceable  statements 
as  to  the  limits  which  theory  imposes  upon  the  development  of 
this  class  of  motor.     Certain  suggestive  equations  bearing  upon 
the  design  and  proportioning  of  cylinders  will  also  result  from 
this  theoretical  treatment. 

It  will  be  necessary,  however,  to  supplement  the  fundamental 
treatment  and  definitions  in  the  first  three  chapters  by  a  brief 
reference  to  the  use  made  in  this  chapter  of  the  diagram  whose 
coordinates  are  the  absolute  temperature  for  ordinates  and  the 
value  of  the  entropy  factor  as  abscissas. 

181.  The  Temperature  Entropy  Diagram. — It  has  been  shown 

in  paragraph  40  that  with  a  piston  motor  the  work  done  in  foot- 

346 


THEORETICAL  ANALYSIS  OF   THE  GAS-ENGINE.  347 

pounds  could  be  conveniently  represented,  graphically,  by  an 
area  of  a  diagram  whose  coordinates  are  the  pressure  in  pounds 
per  square  foot,  as  ordinates,  and  with  the  volumes  in  cubic  feet 
of  the  cylinder  or  piston  displacement  as  abscissas.  Such  a  dia- 
gram is  conveniently  called  the  PV  diagram.  It  shows  at  a  glance 
how  the  work  of  the  motor  varies  with  pressure  and  volume  as 
the  piston  reciprocates,  but  it  shows  nothing  at  all  concerning 
the  variation  of  work  done  as  heat  is  added  or  withdrawn  as  tem- 
perature varies.  If,  on  such  a  diagram,  the  line  representing 
the  increase  of  volume  and  decrease  of  pressure  be  drawn  which 
shall  closely  resemble  the  variation  of  pressure  and  volume  in 
adiabatic  expansion,  it  is  impossible  to  say  whether  the  gas  under- 
going that  expansion  is  gaining  or  losing  heat.  If  the  line  drawn 
is  above  the  computed  adiabatic  line,  the  gas  must  be  receiving 
heat.  If  it  is  below  such  computed  adiabatic  line,  it  is  losing 
heat.  But  in  the  absence  of  such  computation,  the  diagram 
is  silent  concerning  the  gain  or  loss  of  heat  with  temperature. 

It  is  very  necessary  to  know  what  the  action  is  of  a  metal  wall 
on  a  mass  of  expanding  gas  in  the  matter  of  gain  or  loss  of  heat 
energy.  Such  a  method  has  been  proposed  and  is  now  in  quite 
general  use.  It  has  for  its  object  the  presentation  of  a  diagram 
with  two  coordinates,  of  which  one  shall  be  the  absolute  tem- 
perature (conveniently  the  vertical  ordinate)  and  the  abscissa 
or  horizontal  measurement  such  that  the  area  will  show  the  quan- 
tity of  heat  energy  in  British  thermal  units  gained  or  lost  by  the 
gas  during  any  change.  If  the  horizontal  coordinates  be  desig- 
nated by  the  Greek  letter  phi  (<f>)  then  for  any  small  change  in 
the  total  quantity  of  heat  at  a  temperature  T  that  small  gain  or 
loss  in  heat  designated  by  dH  will  become  equal  to  T(d<j>).  It 
has  been  quite  usual  when  the  absolute  temperature  is  associated 
with  0  as  a  coordinate,  that  it  should  be  written  6,  and  the  co- 
ordinates 6  and  <£  give  what  has  been  called  the  theta-phi  dia- 
gram. It  is  capable  of  demonstration  by  the  method  of  the  cal- 
culus that  the  coordinate  (f>  is  the  factor  which  was  designated 
by  Clausius  by  the  name  entropy  as  the  value  for  a  convenient 


348 


THE  GAS-ENGINE. 


factor  made  necessary  by  the  process  of  integration.  This  fact 
gives  to  the  theta-phi  diagram  its  other  name  of  temperature- 
entropy  diagram.  If,  in  Fig.  100  the  curved  line  ab  represents 
an  addition  of  heat  to  a  mass  of  gas  at  a  constant  pressure,  it  will 
be  apparent  that  the  temperature  will  vary  with  such  addition 
of  heat.  For  a  very  small  change  in  the  temperature  d6  it  will 
be  true  to  say  that 


Hence  it  will  be  true  to  write 


and 


FIG.  100. 


FIG.  ioi. 


If  the  value  of  0  be  assumed  constant,  as  it  may  be  during 
any  one  of  the  infinitesimal  theta-phi  diagrams,  the  successive 
elements  of  which  that  change  is  made  up  would  appear  as  in 
Fig.  ioi  so  that  the  whole  change  in  the  quantity  of  heat  due  to 
the  successive  additions  will  be  the  sum  of  all  the  small  elements  or 

[dO~\ 
CP~Q  !• 

If,  obviously,  dO  is  taken  very  small,  the  steps  forming  the 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  349 

broken  line  become  very  short  and  the  change  in  the  value  of 
the  area  under  the  curve  becomes 


•f- 


The  appearance  of  that  quantity  suggests  that  by  the  pro- 
cesses of  the  calculus  the  sum  of  a  number  of  such  infinitesimal 
increases  will  take  the  form 


The  hyperbolic  logarithm  bears  to  the  ordinary  logarithm 
whose  base  is  ten,  the  ratio  of  2.3026,  so  that  in  terms  of  the  com- 
mon logarithms,  this  equation  appears 

182.  Changes  in  Value  of  Phi  when  Heat  is  Added  to  Air. — 

It  will  be  recalled  (par.  54)  that  the  quantity  of  heat  necessary 
to  raise  a  unit  weight  of  air  will  differ  according  to  the  condition 
of  that  air  with  respect  to  the  constant  value  of  pressure  or  volume. 
In  the  foregoing  paragraph  the  pressure  was  assumed  constant 
under  the  addition  of  heat.  Under  this  circumstance 

C*  =  0.2375  B.T.U. 
Substituting  in  the  foregoing  equation, 


If  the  change  be  at  constant  volume,  while  the  pressure  is 
allowed  to  vary,  the  specific  heat  Cv  is  0.169,  so  that  the  equation 
should  be 

ft 


350 


THE   GAS-ENGINE. 


If  the  temperature  remains  constant,  the  addition  of  heat  is 
called  isothermal  (par.  40),  in  which  case 

V 


Inserting  the  appropriate  figures, 


V 


V 


Since  this  last  change  takes  place  at  constant  temperature  of 
the  gas,  it  will  be  apparent  that  the  line  which  is  a  curve  in 
Fig.  100  becomes  a  straight  line,  parallel  to  the  horizontal  axes 
of  coordinates.  If  a  vertical  line  be  drawn  at  any  point  on  that 
horizontal  coordinate  axis,  which  shall  represent  the  value  of  (f>1 
measured  from  the  point  O  and  having  a  vertical  height  equal 
to  the  value  of  the  temperature  T  at  which  the  addition  of  heat 


FIG.  1 02. 

was  made  at  constant  temperature,  the  area  TX(</>2—(i)i)  (Fig. 
102)  will  denote  the  addition  of  heat  which  is  the  quantity  H. 

Finally,  if  the  change  in  pressure  and  volume  be  that  which 
is  designated  as  an  adiabatic  change  (par.  50)  there  will  be,  by 
definition,  no  heat  added  or  subtracted  during  that  expansion 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  351 

or  cnange  of  relation  between  pressure  and  volume.  Under  this 
condition  the  0$  diagram  must  be  such  that  the  area  between 
the  line  representing  this  change  and  the  line  of  zero  tempera- 
ture be  zero.  The  only  way  that  this  can  be  realized  with  a  finite 
value  for  the  temperature  will  be  to  have  the  value  for  the  abscissa 
</>  zero.  Hence  an  adiabatic  line  on  the  plane  of  the  6$  coordi- 
nates is  a  vertical  line. 

183.  Analysis  of  the  Possible  Cycles  of  the  Internal  Combus- 
tion Engine. — By  a  reference  to  paragraph  61,  it  will  be  noted  that 
the  medium  used  in  the  gas-engine  is  subjected  usually,  though 
not  always,  first,  to  a  compression,  then  to  a  heating  process,  and 
that  after  the  heating  the  gas  is  expanded,  doing  work  against  the 
piston  and  is  then  cooled.  This  paragraph  also  presented  a  table 
indicating  the  possible  forms  which  these  processes  might  take, 
which  is  here  reproduced.  In  the  following  diagrams  an  attempt 
has  been  made  to  place  side  by  side  a  typical  work  diagram  with 
the  PV  coordinates  and  a  temperature-entropy  diagram  on  the 
6<j)  coordinates.  In  each  case  the  odd 'number  at  the  left  hand 
is  the  PV  diagram  and  the  even  number  at  the  right  the  corre- 
sponding 0<j>,  for  each  cycle.  For  clearness  of  presentation, 
Figs.  111-151  are  not  drawn  to  the  same  or  to  any  definite  scale. 
For  purposes  of  comparison  of  cycles  a  second  series  of  PV  areas 
on  the  same  scale  for  the  various  cycles  is  presented  in  Figs.  153 
to  161. 

The  cycles  in  the  first  group,  without  compression,  and  the 
cycles  of  the  sixth  to  tenth  groups,  where  the  cyclic  operations 
take  place  at  or  below  atmospheric  pressure,  are  of  insignificant 
importance  in  any  practical  way. 

The  early  gas-engines  previous  to  Otto  (Lenoir,  Barnet,  Hu- 
gon,  Langen,  and  Bischof)  belong  to  this  class,  but  the  introduc- 
tion of  the  compression  so  greatly  increased  the  efficiency  and 
economy  of  the  gas-engine  that  they  do  not  deserve  detailed  con- 
sideration at  this  date.  The  cycle  IB,  for  example,  is  that  of  the 
free  piston  engines,  such  as  Barsanti  and  Matteucci  in  1854  and 
the  Otto  and  Langen  of  1866,  in  which  the  piston  was  not  con- 


352 


THE   GAS-ENGINE. 


nected  positively  to  the  shaft  for  the  expansion  stroke,  but  was 
thrown  freely  upward  to  a  point  beyond  that  at  which  atmospheric 
pressure  would  have  resulted  from  the  increase  of  volume. 


CLASSIFICATION  OF  CYCLES. 


I. 

2. 

3- 

4- 

5- 

6. 

Cycle  No. 

Compression. 

Heating. 

Expansion. 

Cooling. 

Cooling. 

I 

Isometric 

Adiabatic 

Isopiestic 

I  A 

Isometric 

Isot)iestic 

IB 

« 

a 

Isothermal 

I  C 

« 

tt 

II 

Adiabatic 

Isometric 

Adiabatic 

Isopiestic 

II  A! 
II  A2 

« 

tt 

a 

» 

Isometric 

Isopiestic 

II  B 

ft 

u 

" 

Isothermal 

Isopiestic 

IIC 

11 

it 

tt 

III 

Adiabatic 

Isopiestic 

Adiabatic 

Isopiestic 

III  A 

" 

a 

u 

Isometric 

Isopiestic 

III  B 

" 

u 

It 

Isothermal 

" 

me  ' 

tt 

tt 

« 

IV 

Adiabatic 

Isothermal 

Adiabatic 

Isopiestic 

IV  A 

« 

" 

" 

Isometric 

Isopiestic 

IV  B 

" 

" 

" 

Isothermal 

« 

IV  C 

" 

" 

" 

a 

V 

Adiabatic 

Any  law 

Adiabatic 

Isopiestic 

VA 

" 

" 

« 

Isometric 

Isopiestic 

VB 

it 

tt 

'* 

Isothermal 

" 

VC 

(C 

1C 

tt 

n 

VI 

Atmospheric 

Isometric 

Isothermal 

VII 

Adiabatic 

Adiabatic 

Isopiestic 

VIII 

« 

u 

Isothermal 

IX 

Adiabatic 

« 

(( 

Isometric 

X 

tt 

Any  law 

Similarly,  the  cycles  numbered  six  and  upwards  are  of  com- 
paratively slight  importance.  It  would  be,  furthermore,  entirely 
possible  to  make  combinations  or  differentiations  of  the  typical 
cycles  other  than  those  selected  if  it  were  worth  while. 

Let  Fig.  in  be  a  PV  diagram  and  Fig.  112  be  a  6(f>  diagram 
for  the  cycle  of  the  Lenoir  engine. 


THEORETICAL  ANALYSIS   OF  THE  GAS-ENGINE. 


353 


Then  in  this  case: 

From  B  to  C.     Addition  of  heat  isometrically  from  atmos- 
pheric pressure. 

From  C  to  D.     Adiabatic  expansion  to  atmospheric  pressure. 
From  D  to  B.     Cooling  at  atmospheric  pressure. 


Cycle  I 


FIG.  in. 


FIG.  112. 


Cycle  I A 


e 


FIG.  113. 


FIG.  114. 


The  first  modification  would  be  that  in  which  the  expansion 
was  incomplete,  as  in  an  ideal  Lenoir  engine  where  the  cut-off 
was  too  late  to  secure  complete  expansion.  Calling  this  cycle 
I  A,  we  have  Figs.  113  and  114  as  follows: 


354 


THE   GAS-ENGINE. 


In  this  case: 

From  B  to  C.  Addition  of  heat  isometrically  from  atmos- 
pheric pressure. 

From  C  and  D.  Adiabatic  expansion  to  point  above  atmos- 
pheric pressure. 

From  D  and  E.     Cooling  isometrically  to  atmospheric  pressure. 

From  E  to  B.     Cooling  at  atmospheric  pressure. 

The  second  modification  is  that  in  which  the  expansion  goes 
below  atmosphere  before  the  end  of  the  strok  as  in  the  designs 
of  Otto  and  Langen  (1866)  and  Barsanti  and  Matteucci  (1854), 
which  were  called  free-piston  engines.  The  pair  of  diagrams 
will  be  as  follows: 


Cycle  IB 


FIG.  115. 


FIG.  116 


In  these: 

From  B  to  C.  Addition  of  heat  isometrically  from  atmos- 
pheric pressure. 

From  C  to  D.  Adiabatic  expansion  to  below  atmospheric 
pressure. 

From  D  to  E.     Cooling  isothermally  to  atmospheric  pressure. 

From  E  to  B.     Cooling  at  atmospheric  pressure. 

No  engine  has  ever  been  built  to  operate  on  the  third  modifi- 
cation of  this  cycle  in  which  work  is  received  from  the  gas  during 
its  cooling  phase.  Calling  this  cycle  1C,  Figs.  117  and  118  result: 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  355 


Cycle  1C 


FIG.  118. 


Addition  of  heat  isometrically  from  atmos- 
Adiabatic  expansion  to  pressure  below  atmos- 


FIG.  117. 

So  that: 

From  B  to  C. 
pheric  pressure. 

From  C  to  D. 
phere  such  that 

From  D  to  B.  Cooling  isothermally  to  original  volume  and 
atmospheric  pressure. 

The  analysis  for  cycle  /  is  as  follows: 

Let  Hl  be  the  heat  added  from  B  to  C. 

Let  Cv  be  the  specific  heat  of  gas  at  constant  volume,  and 
here  assumed  constant  for  simplification.  It  is  probably  a 
variable,  but  to  make  this  assumption  gives  unmanageable 
formulae.  A  correction  may  afterward  be  applied,  if  desired. 
Ct,  =  heat  to  raise  one  pound  gas  i°  F.  at  constant  volume. 

Let  Vb  be  the  volume  of  the  gases  at  point  B  of  the  diagram, 
i.e.,  before  heating  and  expressed  in  cubic  feet. 

Let  pb  be  the  corresponding  pressure  in  pounds  per  square 
foot. 

Let  Tb  be  the  corresponding  temperature  in  absolute  degrees 
Fahrenheit. 

Then  will  the  increase  in  temperature  be  given  by 


356  THE  GAS-ENGINE. 

or 


<v 

Since  volume  is  constant  from  B  to  C, 

A=rf; 

whence 

Tc 


From  (i), 

£ 

Tb 


Since  this  quantity 

H, 


i+ 


will  enter  into  many  of  the  equations,  let  it  be  denoted  by 

i  +  7^r=^; 
CvTb 

whence 

P< 

The  adiabatic  relation 

Pd 

gives 


^  =  *>cl-7- 


But  pd=pb  by  hypothesis,  hence 

(3) 


THEORETICAL  ANALYSIS  OF   THE  GAS-ENGINE.  357 

Another  adiabatic  relation  gives 


T 

whence 


remembering  pd  =  pb  and  substituting  the  value  of  Tct 


!r\  I  I     7  np   v         T  T*   ~Vy  /    \ 

HlF/       =-^^  =  Z&Ar»       .     .     (4) 

\  / 

Let  H2  be  the  heat  discharged.     Then 


where  CP  =  specific  heat  at  constant  pressure  and  assumed  con- 
stant.        Hence  substituting 

7 -i).  .    .    (5) 


The  work  done  in  heat-units  will  be 

i_ 
=  H1  —  CPTb(Xr—i).      ......     (7) 

And  in  foot-pounds 

TF=y[H,-cpr6(jr7_I)]. 

This  work  of  expansion  could  have  been  obtained  by  tem- 
peratures and  by  integration  as  well. 
The  work  W  will  be: 

W  =  Cv(Tc-Tb)-CP(Td-Tb). 


358  THE  GAS-ENGINE. 

But 

r  -r 

^~^~ 


0 


T  ' 
-' 


.    W-C  T  —C  T  —C  T  4-T  T        I-[  (  P*v*\  T  -L  (Po^o  \~\T 

••  *   -^v1*  —^v*b   uv2  d+^vi  b—-j^(~^  nd+\-^-  ]  \i  b. 


It  is  true  also  that 

t^i.T  - 

T         d~ 

1  o 

Mo  T 

-TfT-  -Lb= 

1-  o 

and 


in  heat-units.    This  second  term  is  the  area  of  the  rectangle  be- 

(  p=o  .  (  v=vt> 

tween-j  \  .       andK  and    lying    below    atmosphere 

(  p  =  atmosphere         (  v  =  vd 

is  not  available  for  work. 

By  integration  W'  =  j,  c  pdv  =  are&  between  expansion  curve 
and  axis  of  volumes.     The  expansion  is  adiabatic. 


A^__A!lTj_ 
A  -vr~     r-rt'L 


Since 


p 

*\  _     ^     /^A 
j     Cv-Cp\Tj 


Cv-CPT 


=JCv(Tc-Td]  in  foot-pounds. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  359 

Subtracting  the  rectangle  pb(vd—Vb),  we  get 


in  foot-pounds,  or  in  heat-units 

W  =  H1-C,Tb(X7-I) 

as  before.  ^; 

Applying  at  this  stage  a  test  to  each  of  the  states  B,  C,  D  from 
the  law  of  perfect  gases: 


Tc       TbX       Tb 


hence  these  are  identities,  as  they  should  be. 

Denote  the  volume  swept  through  or  volume  range  by  Rv. 
Then  will 


-l]  .....      (8) 

Whence  mean  effective  pressure 


.....    (9) 

i%prr--i] 

Efficiency 


~Hr  H;" 

The  entropy  range  is  given  by 

(ii 


THE  GAS-ENGINE. 
Mean  effective  temperature 


The  temperature  range 

TT 

RT=Tc-Tb=j~  .......     (13) 

V 

The  pressure  range 

i)  ......     (14) 


Whence  an  expression  for  a  mean  effective  volume  may  be 
written 

MEV     W    jrtg.-CWT7.-iM 
~~  - 


These  results  are  here  tabulated  for  reference  and  comparison 
with  what  follows: 

It  would  be  possible  to  take  a  set  of  formulas  derived  else- 
where for  mean  effective  temperature,  but  as  these  were  the 
results  of  a  comparison  of  cycles,  none  of  which  ran  below 
atmospheric  pressure,  it  would  be  better  to  take  another  standard 
here.  Taking  arbitrarily  as  the  mean  effective  temperature 
one-half  the  sum  of  the  mean  temperature  of  heat  addition 
and  the  mean  temperature  of  heat  abstraction,  there  results: 

CYCLE  I.    X=i  +  -^-^r. 

^v     b 

Formula  Reduced  to  Initial 
Symbol.  Formula  as  Derived.  Conditions. 

pi Arbitrary pb 

B>* "    * 

B  •  --  pw, 


R  '  £ 


THEORETICAL  ANALYSIS   OF  THE  GAS-ENGINE. 


Symbol. 


Formula  as  Derived. 


Formula  Reduced  to  Initial 
Conditions. 


C  - 

D  < 

W. 

J-  c 

X 
b 
X 

!» 
1 

1 
£r 

l 
r-l) 

»(-^-i) 

1 

7-i) 

»Tb 

fp'Y 

Vd"          'Vc\pJ  i 

\Pc/ 

C//T1                 /Tl    \                                                                            /^*      /7~»      /  \7" 

7  Y  7*7"          7"  7"  N                                   7  (  7"  7"         /"^    T 

w                  i   c,rfe(x 

-"i                            •" 

..ifc-tPL.                           ..^(^TT 

-i) 

M.I 

sr                    /^                 //ff'-c^7 

*'                          \       ^(^7-i) 

M.I 
R+. 

M.I 

Rr. 

LV                              ^                        /(H'-C'T 

1 

_C  log.—.,                         ..C  Ic 

&-y 

6(^"-i) 

,T                       i(Hl+H,\                 i(Hl+Cpl 

~2(  R,  r     "2(    cri< 

..Te-Tb..                        ..Ti(X 

>S,X 

—  il 

362  THE  GAS-ENGINE. 

CYCLE  I.    A. 
As  in  Cycle  I  for  point  C: 

vc  =  vb',       (i) 

.' (2) 

........  (3) 

Assume 

Pc>Pd>Pb* 

Then  from  the  adiabatic  relation 


or 


Also 


Substituting  values  of  pc  and  Tc  in  (4)  and  (5), 


If  it  be  granted  that 

Pb 

jr- 

then 

vd=vb(Xn)7;      .    .    ......    (8) 


T       TY  - 

ld=-LbXrnr  —  --  1         ....      (9) 


.    .  (10) 
..  (n) 


THEORETICAL   ANALYSIS  OF  THE  GAS-ENGINE.  363 

Applying  the  perfect  gas  law  to  the  points  B,  C,  D,  and  E, 


Tc 


i 
p.v,    pbvb(Xn)r  _J? 

Jr==~      —~K- 

e        Tb(Xn)r 

Heat  is  abstracted  in  two  parts,  the  first  at  constant  volume 
from  D  to  E  and  the  second  at  constant  atmospheric  pressure 
from  E  to  B. 

Hence 


(^)7-i.     .   .   .   (12) 

The  work  done  in  foot-pounds  is 


I-  CvTb(Xn)  r-i+  CtTb[(Xn) 


-ffl 


364  THE  GAS-ENGINE. 

The  mean  effective  pressure 


But 


W 
M.E.P.  =  —  ........    (16) 


r  l/i     \  1 

\  HI  -  CvTb(Xn)  r  ( -  - 1  j  +  CPTb[(Xn)  7  - 1]  | 

.-.M.E.P.  =  /j VL-^-        ^(l8) 

I  vJi(Xn)r --L]  J 

W 


__j 


.         (20) 


As  before,  the  entropy  range  is 

R*  =  C\ogeX  ........     (21) 

Taking  the  mean  effective  temperature  as  the  mean  of  the 
average  heating  temperature  and  the  average  cooling  temperature, 


'  (23) 


The  temperature  range  is 

RT=Tc-Tb=Tb(X-i)  ......     (24) 

The  pressure  range  is 

i)     ......    (25) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  365 


Whence 

.E.V.  =  ~ 
RP 


Pb-± 

(26) 


^CvTb(Xn)r    ---i  }-CpTb[(Xn)r-!] 

:J 


Tabulating  these  results: 

CYCLE  I.    A. 

^    Symbol.  Formula  as  First  Derived. 

pb Arbitrary pb 


C« 


D 


£i 


P 


Td 


pbVb  

R  ;•••   R 


Tc r6(i  +  ^) TbX 

t-,,J-bj 


Vd-  .^c(T£)r.  ....<vb(Xri)r 


l_ 
ve vd vb(Xri) r 

T, T£ Tb(Xn)7 


THE  GAS-ENGINE. 
Symbol.  Formula  as  First  Derived. 


E. 


H, 


M.E.P  .....    -. 


RP 


R 


i  — 


Formula  Reduced  to  Initial 
Conditions. 


H 
.vJi(Xn)7- 


n)T-  -  z    -CfTJ[(Xn)T-i] 


n)         -i+CpTi(Xn)7-i] 


i        ] 
~-il 


Tc-Tb  ..................  Tb(X-i). 

CYCLE  I.     B. 

As  the  operations  up  to  the  point  C,  i.e.,  after  addition  of  heat, 
are  the  same  as  in  Cycle  I,  these  results  may  be  assumed: 

^c  =  ^6,        ........     (i) 

........       (2) 

(3) 


HEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  367 

Choose  pd  so  that 

Pb>pd>o  .........     (4) 

Expansion  CD  gives 


Also 


From  the  isothermal  relation  along  Z>£, 


or 

j_  ^ 

pdvb(Xn)  r      vb(Xri)r 

~          ~ 


Applying  the  perfect  gas  law  to  the  various  points, 


-h  1  T"1 

£dfYM\T  b 

b—(Xn)r 

(Xn)7 
..  n         Pbvb 

T  l     ~  Th 

lb 


<„ 


e  =  Pb  by  hypothesis;      .....     (8) 


368  THE  GAS-ENGINE. 

Heat  is  abstracted  in  two  parts,  first,  a  part  isothermally,  and 
second,  a  part  at  atmospheric  pressure.  The  part  abstracted 
isothermally  is  most  easily  calculated  with  the  aid  of  the  6$ 
diagram  and  its  relations. 

The  entropy  range  along  BC  has  been  found  to  be 

rri 

^=^>c-^  =  6yog^  =  C>g^.     .    .    .     (10) 

Now  it  is  evidently  the  same  so  far  as  entropy  range  is  con- 
cerned whether  the  cooling  is  at  constant  pressure  from  E  to  B 
or  heating  is  done  isopiestically  from  B  to  E,  thus 

<  .......     (ii) 


Hence  the  entropy  range  for  the  isothermal  operation  will  be 
given  by 

(12) 
)r7-1]  .....    (13) 

This    latter  isothermal  change  taking  place   at  temperature 
Te=  Td,  the  heat  of  cooling  will  be  given  by 


(14) 

-1  o/ 

Hence  the  total  heat  abstracted  is 

H2  =  Cp(Te-Tb)+Td[cv\ogeX-Cplog]Q  .     .     (15) 
Tb(Xn)7 


But 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  369 


Since 


and 


hence 


I 

—  —I 

r 


The  work  in  foot-pounds  is 


H 


.-.  M.E.P.=y 


i 


.-.  M.E.V.  = 


(19) 

(20) 
(21) 

(22) 


The  mean  effective  temperature  being  the  mean  of  the  heating 
and  cooling  means  is  given  by 


37°  THE  GAS-ENGINE. 

where  R<f>  is  the  same  as  in  previous  cycle. 

i 
/.  M.E.T.=       J 


(23) 


d~^°l/         n     J 

Tabulating : 

CYCLE  I  B. 

Symbol.         Formula  as  First  Derived.  ^""""^Condrdons10  ^^ 


Arbitrary  

^ 

B< 

Th 

PbVb 

Pr  • 

R  
T, 

R 

..PbX 

C 

Tb 

r. 

T(I       Hl] 

4) 

b\  ,c#j 

..........  pb  ^>  PJ  ^>  O 

rd 
V*. 

/Mi 

1 

D 

T 

v\ptr"' 

.                * 

P  • 

Tc(pJ   
..pb.        

n 
pb 

i 

E~ 

T 

r,. 

n 

j.  e.  ... 

n 

THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  37* 


CP(T,-Tb)+  rdc 


-ff. 


I  — 


I  — 


M.E.P. 


=/ 


RP pc-pd"- 

M.E.V. . 


=7 


l      1  x  r  (^)ri     . 

J  J + T6^r~  log-M 


,-a 


V(Xri)r        "I      Tb(Xn)r  \ 

1-c^{-^r-IJ+-VJ-10^ 


>-cr 


M.E.T, 


I 


372  THE  GAS-ENGINE. 

\_ 
P  T       T  Tf         (Xn)rl 

RT  ............  Ti>—Td  ....................  T&l  i—  -  -  —  I 

CYCLE  I  C. 

FIG.  117.  FIG.  118. 

Assume  all  results  to  point  C  from  Cycle  I: 

........     (i) 


(3) 
From  the  adiabatic  CD 


« 


This  adiabatic  must  meet  the  isothermal  from  B  in  point  Z>, 
hence 


Equate  (4)  and  (5), 


d 

±-^r.  (6) 


This  is  the  pressure  at  which  the  isothermal  through  B  will 
meet  the  adiabatic  through  C.    Its  corresponding  volume  is 


(7) 
(8) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  373 

The  heat  abstracted  by  the  isothermal  cooling  is  found  as 
before  from  &4>  relation, 

T 

)      ....      (9) 


Hence 

&-&=£>&*;    ......  '  (10) 

.;.  H2=TbCvlogeX  .......    (ii) 

The  work  done  in  foot-pounds  is 

w=y(ff1-Hj-/(flr1-ricjo&x).    .  .  (12) 

The  efficiency  is 


H, 
E=I^H" 

The  volume  range  is 


The  entropy  range  was  found  R^  =  C^og,X,  hence 

M-E-T-  - 


And 


Hence 

M.E.F. 

i*(.yFi-)i.    :  .    .    .    .    .    (15) 
The  pressure  range  is 

*j--fi,(x  --  V).     •    •    (16) 

Xr-l          \         XT^' 


374 


THE  GAS-ENGINE 


Tabulating : 


Symbol. 


CYCLE  1C. 

Formula  as  First  Derived.  ^^"^Con'dWo'nV0  ^^ 


\pb Atmospheric Atmospheric 


1  ^6- 


1  lb< 


C* 


PC 


D* 


M.E.P. 


Arbitrary 


J* 

.pbY. 


p 


PC- P. 


d 


M.E.V. 


W 


R 


vb 


R 


.vb 


-.TbX 


Tb 


Tc 

w J^H^HI) J(H 

E.  ../-V7-2.  ..i- 


./ 


«*r-3jr 

V         Xr-i 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


375 


Symbol. 


Formula  as  First  Derived. 

n 


Formula  Reduced  to  Initial 
Conditions. 


M.E.T. 


•+Tb 


RT.  ..................  Te-Tb  .................  Tb(X-i) 

The  relatively  poor  showing  of  Cycle  I  and  its  modifications 
with  respect  to  efficiency  and  mean  effective  pressure  as  com- 
pared with  the  compression  cycles  are  the  reasons  for  its  minor 
importance. 

184.  Compression  Cycle  with  Isometric  Heating.  —  This  group 
includes  as  No.  II  A  the  ideal  Otto  cycle,  where  the  gas  is 
heated  and  cooled  at  constant  volume.  The  PFand  d(j>  diagrams 
and  the  mathematical  analysis  are  as  follows: 

The  first  or  typical  case  is  that  of  the  ideal  Atkinson  engine, 
or  some  compound  engines,  with  an  expansion  complete  down  to 
atmospheric  pressure. 

Let  Fig.  119  be  the  PFand  Fig.  120  the  6(f>  diagram  of  this 
cycle. 


Cycle  II 


0 


FIG.  119. 


FIG.  120. 


From   A    to   B.    Adiabatic    compression   from   atmospheric 
pressure. 


376  THE  G/IS-ENGINE. 

From  B  to  C.    Addition  of  heat  isometrically. 

From  C  to  D.    Adiabatic  expansion  to  atmospheric  pressure. 

From  D  to  A.     Cooling  at  atmospheric  pressure. 

In  the  compression  cycles  the  volume  ratio  —  will  enter  into 
many  of  the  formulae  so  that  it  will  be  found  convenient  to  write 


The  compression  is  adiabatic,  hence 


During  addition  of  heat  vc  =  vb,  and  therefore 

T 


rp  TT 

If  -~r  =  i+^r£-  =  X  as  in  the  previous  cycles, 


par'X;   .......    (3) 

Tc=TaT*-lX.    ......     (4) 

Adiabatic  expansion  gives 

^  =  >Uc7  °r  if  ^  =  ^ 


(/>  -y-rv  \  1  IT;          1  1  * 

^JT=^rx7=^-rX7=VoXT.    .    . 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  377 

Applying  the  perfect  gas  law 


& 


d        TaXr 
The  heat  discharged 


d 
The  work  done  is 


=  Cp(Td-Ta)=CPTa(X7-i)  .....     (7) 


W=-Hl-H3=Hl-CfTa(X7-i),      ...    (8) 


W 

E       ~ 


W      JHl-CeTtt(X7-i) 

/  ' 


..  (10) 
.    .  (n) 

(12) 


(14) 


378  THE   GAS-ENGINE. 

CYCLE  II. 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 


.— ;  (;- arbitrary) 


,r< 

PC Pb^r  ' 


•  Vb — 

r 

TC Tb(I+H±.Y rbx 

t-s  ,.-*•  b  / 


R. 


Pa Pa 

1 


Cp(Td-Ta) 


g.+ff.\ 

— 


TXr 


W  ...................  .H,-H2  ..........  Hl-CpTa(X7-I) 


I-  TF^  ...........  I— 


M.E.P J'j- J^        ^ 

Va(Xr-i) 


Symbol. 

R*. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  379 

Formula  as  First  Derived.  Formula  Reduced. 

1 


M.E.V. 


./: 


RT Tc-Ta Ta(rr-lX-i) 

In  Cycle  II  A,  one  case  of  which  is  the  normal  Otto  or  Beau 
de  Rochas  cycle: 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isometrically. 

From  C  to  D.  Adiabatic  expansion  to  pressure  above  atmos- 
phere. 

From  D  to  E.     Cooling  isometrically  to  atmosphere. 

From  E  to  A.     Cooling  at  atmospheric  pressure. 

Let  Fig.  121  be  thePF  and  Fig.  122  the  6<j>  diagram  for  the 
cycle. 


Cycle  II  A 


FIG.  121.  FIG.  122. 

Then,  since  the  compression  is  as  in  Cycle  II, 


(I) 

(2) 


380  THE  G 4S -ENGINE. 

Also  for  C,  the  heat  addition  being  as  before, 


(4) 
(5) 
(6) 


The  point  D  lies  arbitrarily  between  C  and  the  atmospheric  line 
on  the  adiabatic 


From  this  point  two  cases  may  be  considered:  i°,  the  general 
case  where  vd  is  greater  than  va,  and  2°,  a  particular  case  where 
vd  =  v0.  This  latter  results  when  by  reason  of  a  throttling-governor 
action  the  gases  at  the  end  of  expansion  have  the  same  volume 
as  before  compression. 


vd>va    and     pd>pa- 
Then  we  have 

An  \  r 

(8') 
(90 

(10') 

(If) 


f  ;  •  (8) 


T j  —  TaX 


or' 


(9) 


,=  Td-J.     .    (12) 


T'=TaX. 


P.' -Pa    . 


fT*  r >r> 

•*•  •*        • 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  $&i 

Apply  the  perfect  gas  law: 


Heat  is  abstracted  as  follows: 

=  Cv(Td-Te) 

+  CP(Te-Ta  .     .     (13) 


01 


The  work  is  given  by 


-C7-.-,.       (.4) 


2°. 


TaX 


R, 


p/v/    v*P*_p 
T'  ~  Ta  -*• 


=C,Ta[X-i], 


TT  f 

2 


rr-i 


382  THE  GAS-ENGINE. 

Volume  range  is 


>.v=Vd-Vt  =  vd-^    .      (I5) 

:.p.=/-2L/— !^_     (l6) 


(15') 


M.E.p.=y 


H-F) 


Entropy  range  is  the  same  for  both  cases: 

Tr 


Mean  of  mean  temperatures  of  heat  addition  and  abstraction: 


2( 


(18) 


Pressure  range  is  same  for  both  cases, 


Mean  effective  volume: 
M.E.V.=J    ,  ^ r 


(20) 


M.E.V. 


W 


Temperature  range  is  also  the  same  for  both 


(19) 

(20') 
(21) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


3*3 


CYCLE  II  B. 

The  third  type  of  cycle  in  the  second  group  is  one  which  has 
never  been  applied  to  an  actual  engine.  It  gives 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isometrically. 

From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere. 

From  D  to  E.     Cooling  isothermally  to  atmospheric  pressure. 

From  E  to  A.     Cooling  at  atmospheric  pressure. 

Let  Fig.  123  and  Fig.  124  be  the  PV  and  6<j>  diagram  respec- 
tively of  the  cycle. 


Cycle  N  B 


FIG.  123.  FIG.  124. 

Assume  same  results  as  before  up  to  the  point  c.     Take  pd 
something  less  than  atmosphere,  i.e., 

pa>pd>o',        .     .._..;.     ...     (i) 


then 
and 


.       (2) 


\  PC/ 

Tt-Tj-1?^- 


(3) 


THE  GAS-ENGINE. 


Through  D  and  a  point  E  whose  volume  is  greater  than  the 
original  an  isothermal  is  drawn, 


Hence 


Pe-Pa  ............       (6) 

Apply  the  perfect  gas  law  to  the  points 


TC     Tarr-lxr 


dVapa'Xr  =R 

l          \r-l      1 


T 


During  the  isothermal  compression  heat  must  be  abstracted;  the 
amount  can  best  be  calculated  by  6<j>  coordinates.  Call  this 
amount  m,  then 


But 

<l)d~(l)e=  (fa  —  <l>b)  —  (<f>e  — 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  385 

and 


[L/  p\i^l"\ 
Xr(pr\ 


Besides  this  amount  m  a  quantity  CP(Te  —  Ta)  must  be  abstracted 
isopiestically,  whence 


Ht-C,(T.-T.)+  Te   C,\0 


The  volume  range  is 


IF  JW 


.    (7) 
(8) 


(13) 

(I4) 

(15) 


386 


THE  GAS-ENGINE. 


CYCLE  II  C. 

In  the  fourth  type  of  the  second  group,  the  final  temperature 
becomes  equal  to  the  initial  temperature  and  the  cycle  is  closed 
by  an  isothermal  corresponding  to  the  change  of  volume  by 
compression  to  get  back  to  the  state  of  pressure  and  volume 
at  A.  Hence  there  is 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isometrically. 

From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere such  that  we  get 

From  D  to  A.  Cooling  isothermally  to  original  volume  and 
atmospheric  pressure. 

No  engine  has  been  built  to  utilize  this  cycle. 

Let  Fig.  125  be  the  PV  and  Fig.  126  the  6$  diagrams  of 
the  cycle. 


Cycle  II  C 


FIG.  125.  FIG.  126. 

All  values  for  the  compression  and  heat  addition  found  in 
Cycle  II  may  here  be  assumed.  The  point  D  lies  at  the  inter- 
section of  two  curves,  one  an  adiabatic  through  C,  the  other  an 
isothermal  through  A,  and  the  relations  can  be  written.  From 
the  adiabatic  relation 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  387 

From  the  isothermal  relation 

Equating, 


r\  P,  > 


This  is  the  pressure  at  which  the  intersection  will  take  place. 
By  substitution, 

Vd~VJf~l,        .......      (2) 

Td  =  Ta  ........    (3) 

Applying  the  perfect  gas  law  to  JD, 

i 


__ 

Td  JL          "  Ta 

~ 


All  the  heat  is  abstracted  at  constant  temperature  during  the 
compression  D  to  A.  The  entropy  range  is  evidently  the  same 
as  for  heat  addition,  and  this  is 


.........     (4) 

whence 

H2=Ta((j>d-^a)  =  TaCv\ogeXy      ....     (5) 
work 

W-Ht-Hi-Ht-TjCJagJC,    ....     (6) 

H2          TaCv\0g,X 
^t-JTr1-     ~ffT~'      •    •    •    •    •    (7) 

MET  ^ 


388 
whence 


THE  GAS-ENGINE. 


Tabulate. 

Symbol. 


MEV    JW 

J.VJ..J-*.  v.         „ 


CYCLE  II  C. 

Formula  as  First  Derived. 


(9) 


M  E  P  -JW    jH,-TaC,logeX 

*•  '  ' 


1a(;-r-1X-i)     as  before.     ....  (13) 


Formula  Reduced. 


Tc 

Pd 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  389 

Symbol  Formula  as  First  Derived.  Formula  Reduced. 

W H1-H2 H.-TaCJogX 

H2  i-TaCv\ogeX 

E '-^ 7  ~^T 

R, CJogjp Cv\ogeX 

•L  b 


M.E.T. 


\(c^x-T^) 


V-fli  • VbXr-    -- 


ri      i 


M.E.P /^- / 


_ 

RP pc-pd 

MFV  /— 

M.E.V lf^ i  i      r 

/^r Tc  -  Ta 

185.  Compression  Cycle  with  Isopiestic  Heating. — In  this 
third  group  of  cycles  are  included  those  in  which  the  heating 
is  effected  at  constant  pressure.  The  most  notable  example  of 
its  application  to  internal  combustion  heating  was  the  Brayton  en- 
gine of  America  and  the  Simon  engine  of  England.  The  succes- 
sion of  events  is: 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isopiestically. 

From  C  to  D.    Adiabatic  expansion  to  atmospheric  pressure. 

From  D  to  A.     Cooling  at  atmospheric  pressure. 

In  hot-air  engines  it  is  the  cycle  identified  with  the  work  in 
England-of  Sir  Geo.  Cayley,  Dr.  Joule,  and  Sir  William  Thomson 
(1851).  If  the  compression  from  A  to  B  were  isothermal,  and 
also  the  expansion  from  CD,  taking  place  at  constant  tempera- 
ture, the  cycle  would  be  that  of  the  Ericsson  hot-air  engine. 


390 


THE  GAS-ENGINE. 


Let  Fig.  127  be  its  PV  and  Fig.  128  its  6<j>  diagram. 

Cycle  III  0 


v  4» 

FIG.  127.  FIG.  128. 

The  compression  results  of  Cycle  II  may  be  assumed,  hence 


rr\  rr\        v_J  /     \ 

Heat  is  added  isopiestically;  hence  calling  CP  the  specific  heat  at 
constant  pressure, 

TT  /  TT 

£fi_T    I         ,      J±\ 

•*-  b  \    •*•     I""    /~i     r~r* 

P          \       CpTi, 

Write 


CPTb 


(4) 
(5) 

(6) 


Adiabatic  expansion  gives  for  final  pressure  of  one  atmosphere 


r~l 


V\r~ 


(8) 

(9) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  39* 

Apply  the  perfect  gas  law 


=R  as  in  II, 


y 


__ 

T         T  V 

•*•  d          2  a* 

Hence  the  formulae  are  verified. 
Heat  is  abstracted  isopiestically. 
.-.  H,  =  Ct(Td-Ta} 

=  CfTa(Y-i)  =        ;      .....     (10) 

.     (n) 
W          H,_      CfTa(Y-i) 

B=jrr  -nr      ~HT 

Volume  range  is 

^  =  ^-^  =  "a(F-p).      .      .      .      .      .      (13) 

Whence  for  mean  effective  pressure 


M.E.T.  =  -f— 


w 


W 

(14) 


(15) 


2\     R<t>    /~2\       CPlogeY 

A.=A(rr-i),  ._•._...;.•,.  .(17) 


392  THE  GAS-ENGINE. 

Tabulate. 

CYCLE  III. 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 


Va  Va 

r " r 


Tt T.(^-)     Taf- 

pc-... 


Tc 


'C 


pd  .................  A* 


W  ................ 

H2 
E  ..................  -i—T 


R<t> 


r 


TT 

T    I  1  T  yf-^- 

1  ~"~  r  T  I  .................     a' 


a 


R,  .................  vd—  vb  ...................  va(Y  — 


M-E-P  ..............  '  ............... 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  393 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 


M.E.V 


As  in  the  previous  group,  if  the  cut-off  is  late  in  a  Brayton 
cycle,  and  expansion  incomplete,  the  following  modification 
follows  which  will  be  called 

CYCLE  III  A. 

The  first  modification  of  type  in  Group  III  presents  the  follow- 
ing succession,  the  expansion  being  incomplete: 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

Addition  of  heat  isopiestically. 

Adiabatic  expansion  to  pressure  above  atmos- 


From  B  to  C. 
From  C  to  D. 
phere. 

From  D  to  E. 
From  E  to  A. 


Cooling  isometrically  to  atmospheric  pressure. 
Cooling  at  atmospheric  pressure. 
Fig.  129  is  its  PV  and  Fig.  130  its  6<j>  diagram. 
Cycle  IH  A^ 


FIG.  129.  FIG.  130. 

Assume  the  results  of  III  up  to  point  C.    The  point  D  is 
situated  anywhere  on  the  adiabatic  through  C  between  C  and 
atmosphere. 
Write 

Pc>pd>Pa (i) 


394  THE  GAS-ENGINE. 

and 

vd>va.     .    .    ;    .    ;    ...    (2) 

This  latter  (2)  will  not  necessarily  follow  from  (i),  but  where 
it  does  not  hold  the  cycle  is  decidedly  imperfect  and  this  case  is 
riere  neglected,  i.e.,  the  case  where  the  isometric  DE  cuts  the 
adiabatic  AB. 

The  relations  will  be: 


=  P«,     ........    (5) 


Apply  the  perfect  gas  law  to  D  and  E. 

•f  d    d L  d  T> 

T     =  /Y>\r-l~^» 


^  ere 

Ta 


, 

This  verifies  the  formulae. 

Heat  is  abstracted  in  two  parts  and  the  amount  is 

Te-Ta)       ....     (8) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  395 

The  work  done  is 

W-H^H*       (10) 

and  efficiency, 


,   '      .      •      .      (12) 


w  w 

~ 


as  before  for  III  .....     (14) 


M.E.T.=I(^)=i(g^-);   .    .    .    (I5) 
Rp  =  pc  —  pa  =  pa(Tr~I)     as  in  III.      .     .     .     (16) 


As  before  III  the  temperature  range 

CYCLE  III.     B. 

In  the  second  modification  of  Group  III  the  expansion  is 
carried  below  atmosphere,  so  that: 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isopiestically. 

From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere. 

From  D  to  E.     Cooling  isothermally  to  atmospheric  pressure. 

From  E  to  A .     Cooling  at  atmospheric  pressure. 

No  engine  has  as  yet  applied  this  cycle. 


396  THE  GAS-ENGINE. 

Figs.  131  and  132  are  its  diagrams. 

Cycle  111  B 


FIG.  131. 


FIG.  132. 


All  results  of  III  A  up  to  period  D  may  be  assumed  except 
that  pd  which  was  there  arbitrary  and  was  assumed  greater  than  pa 
is  here  less  than  pa,  i.e., 

Pc>Pd>°  .........     (i) 

It  was  found  that: 

V'-V°¥(- 

\  i-  d 

and 

T  .......    (3) 

Through  E  and  D  there  must  pass  an  isothermal  and 

v.>Va,      ........     (4) 

t.  =  P«>      ........     (5) 


r-  1 


(7) 


THEORETICAL  ANALYSIS   OF  THE  GAS-ENGINE.  397 

Applying  the  perfect  gas  law  to  £, 


Heat  abstracted  i°  isothermally  a  quantity  m. 
2°  isopiestically  " 
n=CP(Te-Ta) 


But 


, 


w  w 


(10) 


(15) 


THE  GAS-ENGINE. 
W 


M.E.V.=/ 


(16) 


RT=Tc-Ta=Ta(r^Y-i)    as  before  III.  .    . 


CYCLE  III  C. 

In  the  third  and  last  modification  the  cooling  is  isothermal 
with  varying  pressure  all  below  the  atmosphere,  so  that  an  iso- 
tnermal  line  is  called  for  to  bring  the  gas  back  to  the  state  at  A 
with  respect  to  both  pressure  and  volume.  Hence 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isopiestically. 

From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere such  that  we  get 

From  D  to  A.  Cooling  isothermally  to  original  volume  and 
atmospheric  pressure. 

No  engine  has  as  yet  applied  this  cycle. 

Let  Figs.  133  and  134  be  its  diagrams. 

Cycle  IHC 


FIG.  133.  FIG.  134. 

All  results  to  C  may  be  assumed  as  already  derived.  The  point 
D  is  determined  by  the  intersection  of  the  adiabatic  through  C 
with  the  isothermal  through  A.  From  the  adiabatic  relation 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  399 

From  the  isothermal  relation 


•  -.-.A--      ........    (i) 

Fr~l 

By  substitution 

T^^F"!,      .'.    .....    (2) 

Td=Ta,     .    .    ......    (3) 


W=Hl-H2=H1-TaCP\ogeY,  .    .    .    .    (5) 


^ 


MET  _ 


(6) 


V)>     «...   (8) 

7 


-i]  asinlll.       .    .  (n) 


400  THE  GAS-ENGINE. 

CYCLE  III  C. 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 


Vh  . 

°w  • 

•  fai 

Tb.. 

r 

r 

\w 

.  pb  . 

.  parr 

Vr  . 

Tc 

Tb 

r 

pd" 


Td Ta 

H2 Td(<t>e-<h) TaCp\ogeY 


E i—~ i  — 

R* Cplog£ CJog.Y 


Tb 

MFT  — ( — — — -)  —  ( — — ^-Tl^ 

"2  V     R$     /'  ~2\CplogJ     la) 

R 


M.E.P 4 J  {*>-?*'**•? 

*•  I     K^-f) 


M.E.V 

RT.*  ..TC-TQ 


Rp 


THEORETICAL  ANALYSIS  OF   THE    GAS-ENGINE. 


401 


i85.  Compression    Cycle   with   Isothermal    Heating.  —  The 

fourth  group  of  cycles  includes  that  to  which  Carnot's  name  is 
usually  attached  by  reason  of  the  special  study  which  he  gave  to 
it.  The  special  characteristic  of  the  group  is  the  isothermal 
heating.  The  modern  engine  which  aims  to  operate  on  one  of 
this  group  most  nearly  is  the  Diesel  motor. 

1B  Cycle  IV 


FIG.  135. 


FIG.  136 


Figs.  135  and  136  are  its  diagrams,  in  which 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isothermally. 

From  C  to  D.     Adiabatic  expansion  to  atmospheric  pressure. 

From  D  to  A.     Cooling  at  atmospheric  pressure. 

The  results  already  obtained  may  be  assumed  for  the  com- 
pression, but  beyond  that  new  conditions  arise.  By  isothermal 
heating  the  curve  approaches  the  atmospheric  line  and  there  will 
be  a  certain  quantity  of  heat  which  will  bring  the  isothermal  down 
to  the  atmospheric  line,  leaving  a  subsequent  adiabatic  expansion 
an  impossibility.  This  quantity  of  course  depends  on  the  loca- 
tion of  B,  i.e.,  the  amount  of  previous  compression.  The  higher 
the  previous  compression  the  more  heat  may  be  added  isothermally 
before  reaching  atmospheric  pressure. 


402 


THE   GAS-ENGINE. 


The  quantity  of  heat  which  will  make  adiabatic  expansion 
impossible  and  stop  the  isothermal  on  the  atmospheric  line  can 
best  be  determined  from  #</>  relations.  Denote  this  quantity 


FIG.  155 

On  the  6$  diagram,  Fig.  155,  the  point  3  lies  at  the  inter- 
section of  the  isothermal  2  3  drawn  at  temperature  o  2,  the  com- 
pression temperature  and  the  isopiestic  i  3  drawn  from  atmos- 
pheric temperature  o  i  to  the  intersection  3.  In  each  case  the 
entropy  range  is 

T 


Apply  now  to  the  Cycle  IV, 


(I) 


This  is  the  amount  of  heat  which  will  bring  C  down  to  atmos- 
phere with  no  adiabatic  expansion.  In  order  that  the  cycle  may 
exist  according  to  the  hypothetical  definition  less  heat  must  be 
added  "than  this  quantity  Q.  Hence  the  equation  of  condition 
for  the  existence  of  the  cycle  will  be 

H,<Taf-^CP\^ef-\    .....     (2) 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  403 

or 


A  similar  method  can  be  used  to  find  the  amount  of  expansion 
resulting  pressure  and  volume  after  addition  of  Hl  B.T.U.  of 
t. 

Draw  on  both  diagrams  the  isopiestic  through  the  termination 
of  the  isothermal  and  cutting  the  adiabatic  AB  at  point  C'. 


c 

Then 

-i 


c  -   e 

T  rr~l 


But 


-i 


And  the  amount  of  heat  necessary  for  this  isothermal  expansion 
from  B  to  C, 


4°4  THE  G4S-ENG1NE. 

But 


. 
r      C         c. 


and 


Put 


then  wfll 


That  is  to  say,  starting  at  the  state  B  and  adding  a  quantity  of 
heat  Hlt  isothermally  the  resulting  pressure  is 

Pc=^z  =  ^z-  ........     (3) 

Since 

Pb_  =  ^ 

PC        Vb' 


-ez,    .......     (4) 


(5) 
(6) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  405 

Now 

i . 

—  T1  t '  r*       r~*  \  * 

b\     p v) 

.  z(r-*}_Hi(Cp-cj      gi 

'      \  r 


-cj   nc; 

In  Cycle  III, 

IT 

Y=i 
Hence 


Whence 

v*-™*-1 (7) 

Similarly 


Apply  the  perfect  gas  law, 

paVa 


_ 

Tc      eZrTaTr-> 

Pdvd  ^Pa^geY~1_ 
T         T  PY~I         ' 

2  •*•     K 


verifying  the  formulae. 


W_          CpTa 
~~ 


4°6  THE   G4S-ENGINE. 


M.E.T.=-(^"'  ' 


I  T» 


_  /-    —  j 

MT-  p          rKK          y-"l       ^p-La(e  _  IJ  .       , 

.l«,.F.-Jr—  J-      —  T—      —  -r  -  ,        .      .      (15) 


RT=Tb-Ta=Ta(Tr-1-i)  .....     (18) 
Tabulating  for  Cycle  IV: 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 


r 

^r-i 


T1 
Equation  of  condition.  .H^  5T*log^=r 

-*  a 


eTd(Cp-Cv) 

Pb  Va 

v<  ......................  ^  .................  r 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE  4 

Symbol.  Formula  as  First  Derived.  Formula  Reduced. 

TC rb Taf-^ 

Pd Pa Pa 

/M1  r-i 

v- V<(-pJr "•' 


Td 


M.E.P 


W H,-H2 H,-CpTa(eY^-T.) 

E. i-f^ i-CpTa(eY-l-i) 

H,  H, 


'  Tb'  '  rr~lTa 

T  CH 
M.E.T. . 


2  V      RQ 


rr-iT<jH,+  CpTa(eY-*-i}  1 

2        L  Hi  J 


-c.r^-1-!)-! 
Mr-1-!)    'J 


CYCLE  IV  A. 

In  the  first  modification  of  the  type  '  form  in  Group  IV  the 
expansion  is  not  complete,  so  that: 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.    Addition  of  heat  isothermally. 


4o8 


THE  GAS-ENGINE. 
Adiabatic  expansion  to  pressure  above  atmos- 


From  C  to  D. 
phere. 

From  D  to  E.    Cooling  isometrically  to  atmospheric  pressure. 

From  E  to  A.     Cooling  at  atmospheric  pressure. 

Figs.  137  and  138  are  its  diagrams.     This  is  the  case  for  a 


Cycle  IV  A. 


FIG.  137. 


FIG.  138. 


Diesel  engine  in  which  the  line  of  heating  BC  is  too  long  for  the 
size  of  the  engine  cylinder  to  permit  of  complete  expansion. 

The  results  of  IV  up  to  point  C  may  be  assumed.  The  point 
D  lies  somewhere  on  the  adiabatic  between  C  and  atmosphere 
and  is  subject  to  the  conditions 


Pc>Pd>Pe, 


(i) 

(2) 


Then 


pc\L    va 

^- 

pd 


- 

pae 


vae 


(3) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  4°9 

Similarly 


Apply  the  perfect  gas  law  to  D  and  E: 

i  r- 


The  heat  abstracted  is 


(4) 


(7) 
(8) 

(9) 


THE  GAS-ENGINE. 

M.E.P.=y-—— ^ — ,       .    .    .     (10) 


w 
M.E.v.=y— 4- 


lULT-M^sua/^Si  .  .  (I3) 


2 

(       T~b 

RT=Tb  —  Ta  =  Ta(rr-l  —  i). 

CYCLE  IV  B. 

In  the  second  modification  of  the  fourth  group  the  expansion 
goes  below  atmosphere,  so  that 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isothermally. 

From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere. 

From  D  to  E.     Cooling  isothermally  to  atmospheric  pressure. 

From  E  to  A.     Cooling  at  atmospheric  pressure. 

Let  Figs.  139  and  140  be  its  diagrams. 

The  operations  up  to  C  are  as.  in  IV  and  those  results  may 
be  assumed. 

The  point  D  is  subject  to  the  condition 

Pd<P«>    ••''•"'•    *•••••     (i) 
and  the  point  E  to  the  condition 

vg>va. (2) 

Then 


THEORETICAL  A 'NA LYSIS  OF  THE  GAS-ENGINE.  41 


and 


p    IB 


'-1 


Cycle  IV  B 


(4) 
(5) 

(6) 


FIG.  139.  FIG.  140. 

Following  the  methods  already  adopted,  it  will  be  true  to  write 


But 


TT  TT 

•"!_.     -"l 

7\  ~~  T  rr" 

-t  0         -t  a/ 


4*2  THE   GAS-ENGINE. 


M.E.P.=/ 


(7) 

(8) 


.    .    .    (10) 
W 


,     -ff, 


Tb 

i~,    .  . 

RT=Tb-Ta  =  Ta(rr-l-i)  .....     (16) 

CYCLE  IV  C. 

The  third  modification  in  Group  IV  is  the  cycle  known  as 
the  Carnot  Ideal  Cycle,  in  which  the  temperature  is  carried 
down  to  the  initial  value,  so  that  the  isothermal  will  close  it. 
Hence  there  is 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  isothermally. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


413 


From  C  to  D.  Adiabatic  expansion  to  pressure  below  atmos- 
phere such  that  we  get 

From  D  to  A.  Cooling  isothermally  to  original  volume  and 
rtmospheric  pressure. 

Let  Figs.  141  and  142  be  its  diagrams. 


Cycle  IVC 


FIG.  142. 


FIG.  141. 

Assume  results  up  to  C  as  in  IV. 

The  adiabatic  through  C  must  meet  the  isothermal  through 
A  to  locate  the  point  D. 

From  the  adiabatic  relations, 


From  the  isothermal  relation, 


...  v 


4M  THE  GAS-ENGINE. 

By  substitution, 

*  -  Pa-  pc 

fd~  ez~~~r> V2) 

Td=Ta.     ........     (3) 

By  inspection  it  is  easily  seen  the  periect  gas  law  is  satisfied. 


.    w 

••  «t— p=i. 


r-^-flv-fl^i-.-y,     ....    (5) 


-irr1-^" 


&-»*-%-''<%(«*-•:)» 


M.E.P.-7-  -V-, (8) 


(9) 


M.E.V.-7  —  -r-       r-,   .....  do) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  415 

Tabulating  for  Cycle  IV  C: 

Symbol.                       Formula  as  First  Derived.  Formula  Reduced, 

Pb Pa( 

Vb r  r 


-Vb> 

Equation  of  condition..^  >o, 

*  * 


H, 


eTb(CP-Cv) 

vc ^6~r ~eZ 

PC  r 

Tc Tb Tarr'1 

pd ^z 

vd vaez 

Td Ta 


H2 Ta(<l>d 

W HI- 

E..  ..i- 


H±  HJ 

nj     y* 
-*-  df 


M.E.T .       _ 

2   \        R&       ]  2 


416  THE   GAS-ENGINE. 

Symbol.  Formula  as  First  Derived.  Formula  Reduced, 

M.E.P..  ./— .. 


r 

w 
M.E.V.. 


Tb-Ta 


If  the  adiabatic  compression  and  expansion  be  replaced  by 
isometric  changes  of  temperature,  while  the  heating  and  cooling 
phases  remain  isothermal,  the  cycle  which  results  is  that  of  the 
Stirling  hot-air  engine. 

187.  Compression  Cycle  with  the  Heating  Process  Arbitrary. 
—  A  fifth  group  may  be  formed  from  those  cycles  in  which  the 
heating  process  follows  some  arbitrary  law,  which  does  not  fall 
into  one  of  the  normal  types  heretofore  treated.  That  is,  the 
volume  pressure  and  temperature  may  all  vary  while  heat  is 
being  added.  Such  variations  will  give  the  pv  and  0<j>  dia- 
grams herewith  in  which 

From  A  to  B.  Adiabatic  compression  from  atmospheric 
pressure. 

From  B  to  C.     Addition  of  heat  at  variable  pvT. 

From  C  to  D.     Adiabatic  expansion  to  atmospheric  pressure. 

From  D  to  A.     Cooling  at  atmospheric  pressure. 

Cycles  V,  A,  B,  and  C  may  have  the  same  modification  on 
Cycle  V,  as  II,  A,  B,  and  C  have  on  III,  for  example. 

Let  Figs.  143  and  144  be  the  diagrams  of  the  cycles. 

If  heat  be  added  at  increasing  p,  v,  and  T  the  curves  of  states 
will  lie  somewhere  between  the  isometric  and  isopiestic  on  both 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


417 


diagrams  and  the  cycle  is  somewhere  between  III  and  II.  If 
the  heat  addition  took  place  at  decreasing  p,  increasing  v  and  Tt 
the  curve  of  states  might  lie  between  the  isopiestic  and  the  iso- 
thermal and  the  cycle  lie  between  III  and  IV.  It  is  impossible, 
however,  to  calculate  the  appropriate  set  of  formulae  without  know- 
ing the  law  of  variation  of  states.  The  number  of  ways  of  varia- 
tion is  infinite,  and  while  any  one  might  be  assumed,  nothing 
Cycle  V,  6 


FIG.  143. 


FIG.  144. 


could  be  gained  by  the  calculation  unless  the  law  of  variation 
chosen  was  pre-eminently  simple  or  maintains  in  practice.  What- 
ever it  may  be,  however,  the  previous  discussion  will  enable  it 
to  be  classed  pretty  well  without  entering  much  into  details. 

1 88.  Cycles  with  Atmospheric  Heating. — A  group  of  cycles 
must  be  formed  to  include  those  in  which,  with  or  without  rom- 
pression,  the  gas  is  heated  at  or  below  atmospheric  pressure. 
These  form  groups  from  VI  to  X.  In  Group  VI  there  will  be 

From  A  to  B.    Addition  of  heat  at  atmospheric  pressure 

From  B  to  C.     Cooling  isometrically. 

From  C  to  A.     Adiabatic  compression. 

Let  Figs.  145  and  146  be  the  diagrams  of  the  cycle* 

Heat  being  added  isopiestically, 

TT 

7\_T  •*-_£• 

•*•  o      -La      r~t     » 


4i8 


THE  GAS-ENGINE. 

HI 
^CT 

ft 

Va-f-  = 
•*-  a. 


Cycle  VI 


(i) 

(2) 

(3> 


FIG.  145.  FIG.  146. 

The  point  C  lies  on  the  adiabatic  through  A,  hence 


(4) 


(5) 


The  perfect  gas  law  is  seen  by  inspection  to  be  satisfied: 


H, 


(6) 
(7) 

(8) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  4*9 


z^ 

Ta' 


(9) 


(12) 


M.E.P.-/ 


(14) 


M.E.V.=/- 


=  / 


(i5) 

\  Vn.  > 

M1-*-, 

R<j>=Tb-Ta=Ta(x-i) (16) 

CYCLE  VII. 

In  Cycle  VII  there  will  be 

From  A  to  B.    Addition  of  heat  at  atmospheric  pressure. 
Cycle  VII. 


FIG.  147. 

From  B  to  C.    Adiabatic  expansion. 
From  C  to  D.     Cooling  isopiestically. 
From  D  to  A.     Adiabatic  compression. 
Let  Figs.  147  and  148  be  its  diagrams. 


FIG.  148. 


420  THE  GAS  ENGINE. 

For  B  as  before, 


Tb=Taoc  .........       (3) 

The  point  C  lies  on  an  adiabatic  through  B  and  is  subject  to  the 
condition 

pa>pc>°,       .......  (4) 


But 

^6  =  ^a^. 

Hence 

!^  =  ^  (8) 

^        VC  ' 

Similarly 

^=%  ........      (9) 

ld        ±C 

and 

T-Iz. 
•*     X1 


'^i-,  .    .    (ii) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  421 


,x  as  in  VI  .....     (13) 


=  ^c-^a  =  ~*-I,    ....        (15) 


(17) 


(18) 


RT=Tb-Ta=Ta(x-i)  as  in  VI.     •.    .    .     (19) 


CYCLE  VIII. 

Tn  Cycle  VIII  there  are  three  steps  only,  viz.  : 

From  A  to  B.    Addition  of  heat  at  atmospheric  pressure. 


Cycle  VIM 


e 


FIG.  149. 


FIG.  150. 


From  B  to  C.    Adiabatic  compression  to  such  a  pressure 
that  we  get 

From  C  to  D.     Isothermal  compression  to  original  state. 
Figs.  149  and  150  are  its  diagrams. 


422  THE  GAS-ENGINE. 

It  will  be  true  for  B  that 

vb=vax,     ........     (i) 

Pb  =  pa,          ........       (2) 

Tb=Tax.    .    .    .    .....     (3) 

The  isothermal  through  A  intersects  the  adiabatic  through  B 
to  determine  C. 

From  the  adiabatic 


From  the  isothermal 


But 


r 


(4) 
By  Substitution 

«       Pa 

Pc-—T>  /-x 

= 


....  (6) 

W  =  Hl-TaCplogex,     ......  (7) 

raC,log^ 

Ht  •;,;>•  (8) 

r 

^^-•^a^^a^-1-!),     .....  (9) 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  423 


M.E.P.  = 


(10) 


I  — 


(12) 


M  E  T  - 
M.BH  i  .  - 


- 


Cplogjc 


CjQ&K 


CYCLE  IX. 

In  Cycle  IX  the  expansion  is  incomplete,  calling  for  a  cooling 
at  constant  volume,  so  that 

From  A  to  B.     Addition  of  heat  at  atmospheric  pressure. 
From  B  to  C.    Adiabatic  expansion. 
From  C  to  D.     Cooling  isometrically. 
From  D  to  A.     Compression  adiabatically. 
Let  Figs.  151  and  152  be  its  diagrams. 


Cycle    IX 


FIG.  151.  FIG.  152. 

Up  to  the  point  C  the  results  of  VII  may  be  assumed. 
The  point  D  lies  on  an  adiabatic  through  A  and  is  subject  to 
the  conditions 


Pc>Pd>0, 


424  THE  GAS-ENGINE. 

vd>vi» (3) 

Va\  /V.V  f  Va          r      paPc       PC 

=  =— =r  =     >        (4) 


d 


9  PC       X> 


(6) 


'  •  • 


as  before  ......       (9) 


2 


w 

M.E.P.=7—  —  —  I  -  .,    ....     (12) 


(15) 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  425 

CYCLE  X. 

In  this  cycle,  as  in  the  last  four,  heat  is  added  at  atmospheric 
pressure,  then  follows  adiabatic  expansion,  after  which  heat  is 
abstracted  according  to  some  law  as  yet  undefined.  Adiabatic 
compression  completes  the  cycle.  As  the  law  of  abstraction  of 
heat  is  as  yet  undefined  formulae  cannot  be  derived  for  the  cycle 
and  its  discussion  will  be  left  as  with  Cycle  V. 

Formulae  might  have  been  derived  for  the  imperfect  carrying 
out  of  Cycles  VI,  VII,  VIII,  and  IX,  but  they  are  of  such  slight 
importance  in  practice  that  it  did  not  seem  desirable. 

Besides  the  twenty-two  cycles  considered  there  may  be  others 
due  to  the  combination  or  differentiation  of  these  typical  ones, 
but  the  object  of  this  analysis  will  be  best  accomplished  by  a 
study  of  types,  the  non-typical  or  synthetic  cycles  being  omitted. 
The  method  of  study  here  set  forth,  being  of  universal  application 
to  all  possible  cycles,  will  furnish  means  of  reaching  a  clear  under- 
standing of  any  of  the  unconsidered  cycles  should  need  arise. 

Referring  now  to  the  quantitative  graphical  presentation  of 
the  PV  diagrams  for  the  most  important  first  four  cycles  and 
reproduced  in  Figs.  153  to  161,  it  should  be  observed  that  these 
areas  are  all  derived  from  the  following  data  and  were  plotted 
to  scale  of  twenty  atmospheres  to  one  inch  for  pressures  and  200 
cubic  feet  to  the  inch  for  volumes.  The  illustrations  have  been 
made  by  reducing  the  full-size  drawings  to  one-half  size,  which 
has  therefore  doubled  the  scale.  The  data  for  plotting  were: 

A.  Initial  condition: 

Pressure one  atmosphere 

Temperature 492°  F.  absolute 

Volume 12.4  cubic  feet  (approx. 

B.  Compression,  final  equal  to  -^  initial  volume   and  also  J, 
making  two  cases.  ;J 

The  B.T.U.  added  per  pound  of  air  were  500  for  all  cycles 
except  IV  and  IV  C,  in  which  250  only  were  added,  because 
in  Cycle  IV  a  maximum  of  278  B.T.U.  brings  the  isothermal 


426 


THE  G4S-ENGINE. 


40 
z  "> 

E    UJ 

PRESSURE 
ATMOSPHER 
8 

P 

XB            200             .400                600                800               1000               1200              1400 
VOLUME  IN  CUBIC  FEET. 

Cycle  I 


FIG.  153. 


*x 

*£ 

01  I 

CO     fA 

Si 

QC    ^ 

"••5 

L 

0\B            200               400                600               800              1,000             1,200            1.400             1,® 

VOLUME  IN  CUBIC  FEET. 
Cycle  I  C 

FIG.  154 


ATMOSPHERES. 

§  s  i 

PRESSURE  IN 

&.  .80  £ 

D 

0VA            200                400                600                800               1000              1200              l^ 
VOLUME  IN  CUBIC  FEET. 

Cyc 

X) 
le  II 

FIG.  155. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


42.7 


1UU 

CO 

UJ 

cc 

UJ 

r 

Q. 

PRESSURE  IN  ATMOJ 

§  &  i 

"0                  200                400                600                800           .   1000               1200              1400 
VOLUME  IN  CUBIC  FEET.  ' 

Cycle  II  A2 

FIG.  156. 


200 


600  800  1000 

VOLUME  IN  CUBIC  FEET. 


1200  1400 

Cycle  II  C 


FIG.  157. 


428 


THE  GAS-ENGINE. 


400 


600  800 

VOLUME  IN  CUBIC  FEET. 


1000 


1200 


1400 
Cycle  HI 


FIG.  158. 


4U 

_  CO 

2£  ^| 

~  cc. 

UJ    UJ 

2?  Z20 

\ 

Z>    Q.  -*U 

^o 

\T 

ill    5; 

M 

n 

^ 

-^ 

0                  200                400                600                8( 

X)                1000               1200               1400 

VOLUME  IN  CUBIC  FEET. 
Cycle  HI  C 

FIG.  159. 


«u 

"Z.  ^ 

OL 

UJ    uJ 

OL    T 

11 

o 

PD 

0\A             200                 400                 600                 800                1000               1200               1400 

VOLUME  IN_CUBIC  FEET. 
Cycle  IV 

FIG.  1  60. 

\\ 

B 

•3  ?  00 

„-., 

wfe  ^U 
«  0 

c  5 

£^ 

C 

S 

VA.           ^00                400                600                8C 

10               10 

50              12 

DO              14 

00 

-VOLUME  IN  CUBIC   FEET/                                           Cycle  IV  C 

FIG.  161. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  429 

down  to  atmosphere,  and  the  last  phase,  the  adiabatic  expansion, 
becomes  impossible. 

189.  Comparison  of  Cycles  with  Respect  to  Temperatures 
before  Expansion.  —  Of  the  many  cycles  considered  for  comparison 
only  those  will  be  chosen  that  might  be  called  the  perfect  cycles, 
because  accurately  denned,  and  these  are  Cycles  I,  I  C,  II,  II  A2, 
II  C,  III,  III  C,  IV,  IV  C.  The  atmospheric  cycles  are  of  com- 
paratively little  importance  and  will  be  neglected  in  the  dis- 
cussion. Each  variable  will  be  taken  up  separately,  beginning 
with  temperatures,  and  its  value  examined  in  the  different  cases 
by  formula  and  by  calculated  examples  expressed  in  curves  which 
are  then  the  graphical  formulae.  The  curves  given  are  approxi- 
mately correct,  and  as  the  same  approximation  will  probably 
maintain  for  all  the  cases  the  curves  will  serve  as  well  for  com- 
parison as  if  absolutely  exact.  Two  cases  of  each  are  given,  one 
with  compression  2:1  and  one  with  10  :  i  (volume  ratios).  Call 
the  atmospheric  values  pa,  va,  Ta. 

TEMPERATURES  AFTER  ADDITION  OF  H^  B.T.U. 

Cycle. 


I,  1C.  Tc=TaX==Tai  +  ~  (Fig.  162)     .     (i) 

^v1  «/ 

II,  II  A,  IIC.  Tc=TbX=Tb(i  +  -)    (Fig.  163)     .     (2) 


III,  IIIC.  Tc=TbX=Tbi  +  -  (Fig.  164)          (3) 

IV,IVC.  Tc=Tb.     (Fig.  165)       ....     (4) 

Using  axes  of  Tc  and  H1  it  will  be  observed  that  these  are 
all  straight  lines  passing  through  the  axis  of  temperatures  at  Tb 
above  the  origin  except  in  cycles  (I,  I  C)  where  the  intersection 
is  at  Ta.  These  lines  are  inclined  to  the  axis  of  H  and  make 
with  it  an  angle  a  such  that  in 

I,  1C,  II,  II  A,  IIC  'tana=-£,       .     3     .     .  (5) 


43° 

7,000° 
6,000° 
5,000° 
4,000° 
3,000° 
2,000° 
1,000° 

THE  GAS-ENGINE. 

^ 

FAHR. 

/ 

co 

UJ 
LLl 

ce 
C5 

/ 

X 

Q 

III 

H 

/ 

^ 

O 

CO 

CD 

X 

- 

III 

1- 

X 

X 

HIG 

HEST 
C: 

FEMPE 
fcle  I,  I 

RATU 
C 

=IES 

I 

8,000° 
7,000° 
6,000° 
5,000° 
4,000° 
3,000° 
2sOOO° 
1,000° 
n° 

0             100           200           300           400           500           600           700           800           900         1, 
HEAT  UNITS  ADDED. 

FIG.  162. 

X" 

^X 

/ 

\ 

CO 
HI 

^0•.VX 

/ 

X 

)  DEGRE 

^ 

€ 

^ 

s' 

1- 
3 

/ 

^J> 

£X 

< 

£L 

2 
UJ 

x 

/ 

/ 

1- 

X 

s^ 

HIG 

HEST 
Cycle 

FEMPE 
II,  II  A 

RATU 

«,uc 

^ES 

'0     100    200    300    400    500    600     700    800     900    1,000 

HEAT  UNITS  ADDED. 
FIG.  163. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  431 


8,000V 


7,000° 
6,000° 
5,000° 
4,000° 
3,000° 
2,000° 
t,000° 


HIQHEST 
Cyc 


TEMPERATU 
e  III,  III  C 


0  100          300  300          400  500  6GO  700          800          900         1,000 

HEAT  UNITS  ADDED. 


FIG.  164. 


8,000 
7,000 
6,000 
5,000 

4,000 
3,000 

/ 

LA 

*GEST 
Cycl 

VOLU 
si  C 

1ES 

/ 

/ 

jj 

LL 

/ 

5 

0 

/ 

2,000 

/ 

1,000 

^ 

/ 

0, 

- 

^^ 

^ 

xw           saw           300           400           500           600           700           800          'goo     "To<X 
HEAT  UNITS  ADDED. 

FIG.  165. 


432 

and  in 
III,  III  C 


THE  G4S-ENGINE. 


(6) 


while  IV,  IV  C  are  lines  parallel  to  axis  Ht. 

190.  Comparison  of  Cycles  with  Respect  to  Temperatures 
after  Expansion. — A  treatment  similar  to  the  foregoing  respecting 
temperatures  after  expansion  gives  the  following  comparison 
diagram. 


4000 


3000 


2000 


1000 


soo 


HO. 


TEMPERATURES 
AFTER  EXPANSION 

F'^.166 


.  1C.    IIC. 
"IIIC.    JVC. 


100   200   300  400   500  600   700  800   900  1000 

HEAT  UNITS  ADDED 
FIG.  166. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  433 

Cycle. 

i  /          ff    \  l 

r  T1  T«    /V\~          T>    I  I  1       IT  /  < 

I.                               Td-T.(X)r  =  Tb(I  +  ^-Jr,    ....      (I9) 
1C.  Td=Ta, (20) 

r=ra(I+^)f, .  .  .  . 

\         <-,,^6/ 
Hi 


ii.  rd 

•  ^& 


II  A. 


np  T  —T 

^-  -td~-'a> 


rr     \ 

in  ^=r  F=r  d+— • M 

c1,^ 


me.  rd=ra, 


H, 


TV                            T  —  T  pY — i  —  7"1  pG ^ T-L  t rtf\\ 

1V-  ±  i—±ae        —2aepbj ^20; 

iv c.  T^=TV.    ':•';•:•  ...  |  (27) 

Curves  (19)  and  (21)  are  similar  in  form,  cutting  axis  Td  at 
different  points,  however,  and  having  different  slopes.  It  is 
easily  seen  that  (21)  is  always  greater  than  (19),  also  that  (22) 
is  greater  than  (21),  since 


Both  (22)  and  (24)  are  straight  lines,  but  they  have  different 
slopes  through  intersecting  axis  Td  at  the  same  point: 

T1 

(tan  3)IL  h=f=r~  =    r-ir  ,      ....     (28) 


.....     (29) 


434  THE  GAS-ENGINE. 

whence  (22)  is  always  greater  than  (24).  Equation  (26)  is  an 
exponential  cutting  Td  axis  at  Ta.  It  is  concave  up  and  slopes  up 
to  the  right,  since 


(30) 

<PT  i 


These  curves  are  shown  in  Fig.  166  for  the  two  cases. 

191.  Deductions  from  the  Comparisons  of  Temperature.  — 

Translating  and  analyzing  these  equations,  the  following  deduc- 
tions seem  unavoidable: 

1.  For  the  same  previous  compression  the  temperature  result- 
ing in  each  cycle  from  heat  addition,  and  which  is  the  maximum 
for  the  cycle,  will  be  different.     That  is,  the  addition  of  the 
same  amount  of  heat  will  result  in  a  different  temperature  for 
each  group  of  cycles. 

2.  Gases  passing  through   Cycle  I  may,   on  addition  of  a 
certain  amount  of  heat,  H^  have  a  temperature  equal  to  what 
the  same  gas  would  have  passing  through  Cycle  III.    However, 
for  more  heat  added  the  temperature  for  I  will  become  higher 
than  that  for  III,  while  for  less  heat  added  III  will  be  higher. 

3.  Increase  of  compression  before  heating  changes  the  tem- 
perature after  heating  by  only  so  much  numerically  as  the  varied 
compression  has   resulted   in   changing  the   temperature   before 
heating  begins. 

4.  The  temperature  increase  due  to  heating  is  proportional 
to  the  amount  of  heat  added  Hlt  and  the  constant  of  proportionality 
involves  the  reciprocal  of  the  specific  heat  for  the  process  and  the 
weight  of  the  gas  present. 

5.  After  the  gas  has  expanded  to  the  greatest  volume  possible 
in  the  cycle,  no  two  cycles  will  leave  the  gas  with  the  same  tem- 
perature except  in  a  few  special  cases. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  435 

6.  Cycle  I  C,  II  C,  III  C,  IV  C  by  definition  have  the  same 
temperatures  at  the  end  of  expansion,  and  this  is  moreover  con- 
stant no  matter  what  H  may  be  and  is  equal  to  the  initial  tem- 
perature of  the  cycle. 

7.  There  will  be  a  value  of  Hl  for  a  limited  range  of  com- 
pressions for  which  Cycle  III  may  give  to  the  gas  the  same  final 
expansion  temperature  as  Cycle  I. 

8.  Similarly  II  for  one  compression  may  coincide  in  final  tem- 
perature with  II  A  for  some  other  compression. 

9.  The  temperature  after  expansion  for  Cycle  II  Ax  will  always 
be  higher  than  for  III  and  III  higher  than  for  II. 

10.  In  round  numbers  II  A  may  be  25  per  cent  higher  than  III, 
and  may  even  be  100  per  cent  higher  than  II  for  the  same  com- 
pression for  possitxe  values  of  H±. 

1 1 .  With  variation  of  compression  the   temperature   at  the 
termination  of  expansion  will  vary,  always  becoming  lower,  but 
the  extent  of  the  lowering  will  depend  on  how  much  heat  was 
added  before  expansion  and  in  case  II  A  and  III  is  exactly  pro- 
portional to  HI. 

12.  A  change  of  compression  J  to  ^  may  change  the  tem- 
perature at  the  end  of  expansion  in  the  case  of  Cycle  II  A  and 
III  as  much  as  80  per  cent  for  possible  values  of  H±. 

13.  Mean  effective  •  temperatures,  Fig.  167,  are  different  for 
different  cycles  and  for  different  compressions  in  the  same  cycle. 

14.  Cycle  IV  C  is  the  only  cycle  with  constant  mean  effective 
temperature. 

15.  Mean  effective  temperatures  of  all  other  cycles  increase 
with  HI. 

1 6.  For  large  values  of  H1  the  order  of  magnitude  of  mean 
effective  temperatures  will  be:   Lowest,  IV  C,  III  C,  I  C,  II  C, 
III,  I,  II,  highest,  II  A. 

17.  For  lower  values  of  Hl  this  order  may  be   somewhat 
changed,  and  there  will  be  points  at  which  two  different  cycles 
will  have  simultaneous  values  of  M.E.T.  and  H   • " 


THE   GAS-ENGINE. 


The  following  graphical  comparison  of  mean  effective  tem- 
peratures in  the  various  cycles  is  also  instructive  (Fig.  167): 


2,200° 
2,000° 
1,800° 

ui  1,600° 

j  _ 

O  1,400 

< 

u:  1,200° 
S 

w,  1,000 

% 

%  800° 
600' 
400° 
200° 


MEAN  EFFECTIVE 
TEMPERATURES 


in  cu 


iv  0:2 


-IVC.1 


100   200  300  400   500  600  700  800  900  1,000 

HEAT  UNITS  ADDED. 
FIG.  167. 

192.  Comparison  of  Cycles  with  Respect  to  Pressures  after 
Addition  of  Heat  before  Expansion. — A  similar  treatment  of 
the  equations  and  plotting  of  the  pressures  after  addition  of  Hl 
give  the  following  comparison  (Figs.  168-170): 


CO 

UI 

HIGt 

HEST  F 
Cycle 

RESSL 
I;  1C 

RES 

^  *~ 

^^ 

LJ 

I 

Q. 

co 
O 

^ 

^ 

^-e^ 

--—•"^ 

2 

1- 
< 

^^ 

" 

0             JJOO           200           300           400           500           GOO           700           800           900         1,0 
HEAT  UNITS  ADDED. 

FIG.  168. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  437 


1GO 


140 


120 


100 


GO 


HIGHEST 
Cycle  II;  I 


PRESSURES 
I  A2;  II  C 


400     500     600     700     800    900    1,000 

HEAT  UNITS  ADD.ED. 
FIG.  169. 


•20 
15 
10 
5 

COMPRESSION  10: 

1 

'HERES. 

HIGl 
Cycle 

HEST  RRESSL 
III;  III  C;  IV, 

RES 
IV  C 

ATMOSF 

COMPRE 

SSION  2: 

1 

HEAT  UNITS  ADDED. 


FIG.  170. 


43S  THE  G/tS-ENGINE. 

Cycle 

-  (Fig.i68)     .       (7) 


II,  II  A,  IIC.          pc  =  pbX  =  pbi+  (Fig.  169)      .       (8) 

III,  IIIC.  pc  =  pb          (Fig.  170)  .......       (9) 

IV,IVC.  Pc  =  £—    -£r-        (Fig.  170).      .     .     (10) 

e(Cp-Cv}Tb 

Equations  (7),  (8),  and  (9)  are  all  straight  lines,  (9)  bein£ 
parallel  to  axis  Hlt  while  (7)  and  (8)  are  inclined.  Equation  (10) 
is  an  exponential  curve  sloping  down  to  the  right  and  concave 
up  and  asymptotic  to  axis  of  H,  as  can  be  seen  from  the  deriva- 
tives 


dH, 

d2p  pb 


(12) 


193.  Comparison  of  Cycles  with  Respect  to  Pressures  after 
Expansion. — A  similar  treatment  for  the  pressures  after  expan- 
sion gives  the  curves  and  equations  which  follow: 

Cycle. 
I-  Pt-fa          


ic.  A-A--        pa 


II. 


II  A.  P^PaX-pafl  +  c-f. 


IIC. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 

Pa  Pa 

Pd~          1     : 

Xr-i 


439 
(36) 


CURVE  CYCLE  CASE 

I 1C. 

II II  C 1 

III . kt 2 

IV III  C 2 

v :* i 

VII IV  C 1 

VIII '.» 2 

IX II  A 1 

X !i 2 

XI I;  II;  III;  IV > 


200     400     600      800    .1,000  1,200 


200  300  400 

HEAT  UNITS  ADDED. 


500 


600 


FIG.  171. 


III. 

me. 


Pa 

vo// 
<iX\ 

•-1 


440 
IV. 


THE  GAS-ENGINE. 


(39) 


IV  C. 


(40) 


e(Cp-Cv)Tb 


Equations  (32),  (34),  (37),  (39)  are  identical  and  represent  a 
straight  line  parallel  to  axis  H^.  Curve  (55)  is  a  straight  line 
inclined  to  Ht.  All  the  others  are  concave  up,  sloping  down  to 
the  right;  their  relative  positions  are  seen  in  Fig.  171  for  two 
compressions. 

194.  Comparison  of  Mean  Effective  Pressures  in  the  Various 
Cycles. — The  mean  effective  pressure  during  the  working-stroke 
of  the  engine  is  one  of  the  most  impojtant  practical  data  concerning 
the  cycle  under  which  it  is  working.  The  larger  this  value  the 
smaller  the  volume  of  the  cylinder  need  to  be  for  a  given  power, 
and  the  lighter  the  weight  of  the  engine.  The  following  graphical 
presentation  of  the  comparison  of  cycles  in  this  respect  is 
most  instructive  (Figs.  172  to  178).  The  superiority  of  Cycle 
II  A,j  (the  Otto)  is  manifest.  A  statement  of  the  conclusion  with 
respect  to  the  pressures  in  the  various  cycles  must  include  the 
following  conclusions  on  page  387. 


500 
400 
300 
200 
100 

( 

Bl 

^^ 

^^ 

>RESSUR 

^ 

^ 

1CTIVE  1 

^ 

" 

u. 

LL. 
UJ 

z 

/ 

' 

MEAf 

sj  EFFECTIVE 
pycle  I 

PRESS 

JURE 

5 

)             100           200           300           400           600           600           700           800           900         1,0 
HEAT  UNITS  ADDED. 

FIG.  172. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  44 1 


qsn 

V 

\ 

MEA 

^  EFFE 

CTIVE 
ycle  I 

PRESS 

4 

>URE 

250 

\ 

200 

\ 

X. 

-IRA 

\ 

\ 

100 

1 

^ 

\ 

^^ 

^ 

0 

200  300  400  500  600  VOO 

HEAT  UNITS  ADDED. 


16,000 


14,000 


12,000 


10,000 


8,000 


6,000 


4,000 


2,000 


900         1,000 


FIG.  173. 


MEAN  EFFECTIVE  PRESSURE 
Cycle  II 


0  100  200  300  400  500  600  700  800  900         1,000 

HEAT  UNITS  ADDEO. 


FIG  1*74. 


THE  GAS-ENGINE. 


200 


"0  100          800          300          400          500          600          700          800          900         1.000 

HEAT  UNITS  ADDE.D. 


FIG.  175. 


400,000 
350,000 
300,000 
250,000 
200,000 
150,000 
100,000 
50,000 

°( 

1 

X 

MEAI 

\  EFFE 
Cycle 

CTIVE 

n  As 

PRES! 

JURE 

x 

ui 
<r 

1 

X 

01 
QC 
Q. 

01 

^/ 

X 

H 
0 
Ol 
LL. 

O. 

^ 

z 

01 

X 

X 

X 

x 

_ 



_COMP] 

CESSION 

2:1 

~ 

.  —  —  — 

— 

100           800           300          400           500          600           700           800           900         1,W 
HEAT  UNITS  ADDED. 

FIG.  176. 


COMPRESSION 


Jycle  HI 


100  200 


300 


400  500  600 

HEAT  UNITS  ADDED. 


700 


800  900  1000 


FIG.  177. 


2,000 
1,750 
1,500 
1,250 
1,000 
750 
500 
250 

\ 

\ 

MI 

:AN  EFF 

ECTIVE 
Cycle  IV 

PRESSU 

RE 

PESSURE. 

-ECTIVE  P 

U. 

UJ 

Z 
UJ 

5 

\ 

\ 

1 

100  200  300  400 

HEAT  UNITS  ADDED. 
FIG.  179. 


500 


444 

2,500 
2,000 
1,500 
1,000 
500 


THE  GAS-ENGINE. 


MEA 


M  EFFECTIVE 
'cle  HI 


PRESSURE 


100 


200 


400  500  600 

HEAT  UNITS  ADDED. 
FIG.  178. 


700 


800 


900         1,000 


4750 
1500 
1250 
1000 
750 
500 

\ 

Ul 

OB 
=> 

\ 

CO 

u 

cr 

0. 
UJ 

\ 

p. 
n 

I 

u_ 

E 
ul 

z 

\ 

2 

S 

COMPRESSIO 
2M 

1 

\ 

c 

^cle  IV  C 

100  200 

HEAT  UNITS  ADDED. 


1QO 


FlG.  1 80. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  445 

PRESSURES  (Figs.  168  to  180). 

1.  The  pressures  resulting  from  heat  addition  are  different 
for  cycles  with  different  numerals,  but  the  same  in  any  one  group. 
Thus  II,  II  A,  II  B,  II  C  or  Group  II  will  all  have  the  same  pres- 
sures, whereas  those  of  Group  II  will  differ  from  those  of  Groups 

III  and  IV. 

2.  Lines  representing  pressures  as  functions  of  the  heat  sup- 
plied, Hlt  will  cross  as  these  functions  are  different  for  different 
groups,  and  it  will  hence  be  possible  for  the  different  groups  of 
cycles  to  have  the  same  pressures  for  certain  values  of  Hlm 

3.  Groups  I  and  II  have  pressures  after  heating  that  increase 
with  Hlt  while  in  Group  III  the  pressure  is  constant  and  in  IV 
decreasing  with  increase  of  H^ 

4.  For  same  compressions  Group  II  will  always  have  the  high- 
est pressure  after  heating,  and  III,  IV,  and  I  come  in  the  order 
named  for  moderate  Hlt  while  for  large  H1  IV  cannot  exist. 

5.  Increase  of  compression  will  change  the  pressure  after  heat- 
ing in  Group  III  only  so  much  as  results  from  the  changed  com- 
pression before  heating.     In  Groups  II  and  I  the  change  is  such 
-as  to  keep  the  pressure  ratio  before  and  after  heating  constant; 
so  that  for  a  given  change  in  Hl  the  resulting  pressure  change  in 
II  will  be  greatest  for  high  compressions,  less  for  moderate  com- 
pressions, and  least  for  no  compression,  i.e.,  for  Group  I. 

6.  After  expansion  by  definition  the  pressures  of  I,  II,  III,  and 

IV  are  all  atmospheric  and  equal. 

7.  The  pressure  which  II  A2  will  reach  when  the  gas  has 
expanded  to  original  volume  increases  with  Hl  and  is  such  that 
the  ratio  of  this  pressure  to  atmospheric  is  the  same  as  the  ratio  of 
pressure  after  heating  to  that  before. 

8.  Cycles  with  letter  C  all  go  below  atmosphere  in  expanding 
to  such  a  pressure  as  will  bring  the  temperature  down  to  that 
originally  existing  in  the  gas.     These  resulting  pressures  after 
expansion  are  different  for  each  cycle,  but  the  lines  representing 
them  as  functions  of  Hl  may  intersect. 


446  THE  GAS-ENGINE. 

9.  The  lines  for  IV  C  may  cross  others,  but  I  C,  II  C,  III  C 
cannot  intersect,  and  these  will  always  be  in  the  order  of  magni- 
tude II  C,  III  C,  I  C,  and  all  asymptotic  to  axis  of  Hly  so  that  the 
terminal  pressure  can  never  be  zero. 

10.  An  increase  of  compression  will  cause  an  increase  in  final 
pressure  for  same  H^ 

1 1 .  Mean  effective  pressure  expressed  as  a  function  of  H^  will 
give  for  every  cycle  and  every  different  compression  a  different 
M.E.P.  curve,  lut  as  before  these  may  intersect. 

12.  For  all  cycles  except  those  ending  with  isothermal  return 
to  the  original  state,  the  M.E.P.  increases  with  H1}  but  for  those 
bearing  the  letter  C  the  M.E.P.  decreases  and  for  no  cycle  is  it 
constant. 

13.  For  the  same  previous  compression  the  cycles  have  M.E.P. 
of  about  the  following  order  of  magnitude  when  Hl  is  large 
enough. 

Greatest  M.E.P.,  II  A2,  200;  II,  40;  I,  25;  III,  15;  II  C, 
1.5;  I  C,  0.3;  III  C,  0.2.  When  H^  is  small  IV  will -probably 
come  between  III  and  II  C. 

14.  A  change  in  compression  from  J  to  TIQ  (vols.)  may  cause  a 
change  in  II  A2  of  35  per  cent,  II  of  100  per  cent,  III  of  300  per 
cent  for  the  same  possible  values  of  H^. 

15.  The  effect  of  changed  compression  before  heating  is  the 
more  marked  on  M.E.P.  resulting  when  M.E.P.  is  lowest  and  the 
extent  of  the  increase  is  greater  with  Hr 

195.  Comparison  of  Cycles  with  Respect  to  Volumes  After 
Heating. — Following  the  analysis  of  the  effects  of  temperatures 
and  pressures  comes  naturally  a  comparison  of  the  volumes  filled 
when  a  unit  of  heat  is  added  in  the  various  cycles.  The  following- 
lines  show  this  relation  graphically  for  the  phase  of  heating  the  gas: 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 
VOLUMES  AFTER  HEATING  BY  H19  B.T.U. 


447 


100  200  300  400  500  600  700  800  900  1000 

HEAT  UNITS  ADDED. 

FIG.  181. 


1, 1C. 

II,  II  A,  II  C. 

III,  III  C. 


112. 

me  a. 

III.  II A 1.  11C1. 
2.  II A2.  II C2. 

1500 


(13) 
(14) 

dS) 


IV,  IV  C. 


z  =       C 


(16) 


Formula  (13)  is  a  straight  line  parallel  to  Hl  and  is  always  less 
than  (14),  which  is  similar,  but  cuts  axis  of  Vc  at  a  point  vb  higher 
than  va.  Equation  (15)  is  a  straight  line  inclined  to  Hr  Equa- 
tion (16)  is  an  exponential  curve  cutting  axis  Vc  at  point  F&;  it  is 


443  THE   GAS-ENGINE. 

concave  up  arid  slopes  up  to  the  right  as  is  shown  by  the  deriva- 
tives 

-  dvc  vb  . HI 


vb 


(Cp-Cv)Tbt         .       .       .       (i£ 


dH,     (CP-C^ 

These  curves  are  shown  in  Fig.  179  for  the  two  cases. 

196.  Comparison  of  Cycles  with  Respect  to  Volumes  Aftei 
Expansion. — A  similar  treatment  gives  the  following  plotted 
curves,(Figs.  182-189)  for  volumes  after  expansion: 

VOLUMES  AFTER  EXPANSION. 

Cycle. 

1  /  H.    \L 

I.  Vd  =  VaX7=vati  +  ^  )r       (Fig.  182)       .      .       (41) 

\          ^v^  a' 

(42) 


1  ^. 

\          CvTa] 

_L      .  /        HI\-    /«. 

. 

II  A. 

Vd      VaX  ?      {Va[I-\-^,rr>\T        (Fig.  184) 
\          ^v-Lb/ 

vj-vn     (Const.) 

nf* 

1                           TT         1 

u. 
III. 

V                      V       ^/ 

vd-v.Y    (Fig.  186)      .  ,.    .    . 

TTT  r* 

i            .         H   \    r 

n,           n,    Vr       1          o,     /-r     1                  l      \r       1         /T?,'nr      -rZ*\ 

(44) 


(46) 

(47) 

\         ^p-1-*/ 

IV.  vd  =  vaeY-l=vae^      (Fig.  188) .     .     (48) 


These  curves  will  admit  of  considerable  discussion,  but  the  curves 
of  Figs.  182  to  189  show  at  a  glance  all  which  it  is  necessary  to 
know  in  general. 


THEORETICAL  ANALYSIS   OF   THE   GAS  ENGINE  447 


bU 
70 
GO 
50 
40 

yo 
so 

10 

0 

s 

// 

^ 

^ 

/ 

^ 

1- 

LJ 

III 

LL. 

x 

x^ 

0 

5 

3 

/ 

x 

/ 

LA 

IGESTIVOLUI 
Cycel 

/IES 

200     300    400     500     600    700    800     900    1,000 

HEAT  UNITS  ADDED. 
FIG.  182. 


7,000 
6,000 
5,000 
4,000 
3,000 
2,000 
1,000 
0 

/ 

LAI 

\GEST 
Cycl 

VOLUI 

5  I    C 

/IES 

/ 

/ 

/ 

'* 

£ 
Id 

ML 

/ 

o 

5 

z> 
o 

/ 

/ 

/ 

/ 

X 

^  —  * 

'**** 

^ 

100     ^00     300    400     500    GOO    700     800     900    1,000 

HEAT  UNITS  ADDED. 
FIG   183. 


45° 


THE  GAS-ENGINE. 


60 


50 


LARGEST 


VOLUMES 


Cyc  e  II 


09; 


20 


10 


0  100  200  300          400  500  600  700  800  900         1,000 

HEAT  UNITS  ADDED. 

FlG.  184 
4tOOO 


3,500 


3,000 


2,500 


2,000 


1,500 


3,000 


500 


LA 


GEST 
Cyclt 


VOLUMES 
II  C 


'0  UOO          200 


500          600 

HEAT  UNITS  ADDED. 
FIG.  185. 


900        1,000 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE. 


80 


70 


•CO 


50 


40 


30 


20 


10 


16,000 

15,000 

14,000 

13,000 

12,000 

11,000 

10,000 

9,000 

8,000 

7,000 

6,000 

5,000 

4,000 

3,000 

2,000 

1,000 


LARGEST 
Cycl 


VOLUMES 
3  III 


100          200  300          400  500  600 

HEAT  UNITS  ADDED. 
FIG.  186. 


700 


800 


900 


1,009 


LAF 


GEST 
Cycle 


VOLUMES 
III  C 


400          500          gOO          700 

HEAT  UNITS  ADDED. 
FIG.  187. 


900    1,000 


452 


THE   GAS-ENGINE. 


197.  Deductions  from  Comparisons  of  Cycles  with  Respect 
to  Volumes. — In  Fig.  188  is  presented  a  graphical  comparison 
of  mean  effective  volumes  for  certain  cases  of  Cycles  I,  II,  and  III. 
A  statement  of  the  conclusions  capable  of  being  drawn  from  the 
Curves  would  give  (Figs.  188  to  190): 

i.  The  volumes  after  heating  are  the  same  for  cycles  of  the 
same  group,  and  for  all  groups  increase  with  H1  except  in  Groups 


*w 
350 
300 
250 
200 
150 
100 
50 

° 

/ 

/ 

LAI 

tGEST 
Cycl 

voLur 

5  IV 

1ES 

/ 

f 

111 
UJ- 

u. 

/ 

o 
• 

:D 

0 

__..•-._ 

/ 

-A 

/ 

f 

L^2 

\ 

G 

^ 

^ 

cO* 

^ 



^^ 

I2j> 

>            100          -200           300          400           500          600           700          800           900        1,(X 
HEAT  UNITS  ADDED. 

FIG.  188. 

I  and  II,  where  by  definition  they  are  constant  and  equal  to  the 
volumes  existing  before  heating. 

2.  In  Group  III  the  volumes  after  heating  are  proportional  co 
Hl  with  the  same  constant  of  proportionality  for  the  same  com- 
pression.    Increase  of  compression  decreases  this  constant  of  pro 
portionality. 

3.  In  Group  IV  the  volumes  increase  rapidly  with  H^  but  are 
not  proportional  to  H±  so  long  as  H^  is  small;  with  large  H t  Group 
IV  cannot  exist. 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE. 


453 


4.  Lines  of  volumes  after  heating  lepresented  as  functions  of 
Hi  may  cross  in  some  cases.  II,  IV,  and  III  may  cross  I,  i.e.,  the 
compression  cycles  may  cross  the  non-compression  ones.  But  for 
the  same  compression  II,  III,  and  IV  can  never  have  the  same 
volumes  after  heating.  Lines  of  III  and  IV  for  high  compres- 


400 


800 


-250 


150 


TOO 


50 


LARGEST  VOLUMES 
Cycle  IV  C 


100  200  300 

HEAT  UNITS  ADDED. 


400 


500 


FIG.  189. 

sion  may  cross  II  for  a  lower  compression,  but  cannot  cross  each 
other. 

5.  For  possible  values  of  H*L  the  volumes  after  heating  for  the 
different  groups  may  have  the  following  order  of  magnitude  if  Hv 
Is  large  enough:  Group  III,  55.00;  Group  1, 12.38;  Group  II,  6.00. 

6.  After  expansion  is  completed  the  volume  occupied  by  the 


454 


THE   GAS-ENGINE. 


gas  in  the  different  cycles  will  vary  through  very  wide  limits, 
increasing  with  Hr 

7.  The  volume  occupied  by  Cycle  III  will  be  such  as  to  keep 
the  ratio  between  this  final  volume  and  the  volume  before  com- 


100 

90 


I- 
ui 

UJ 

I5" 

•O  40 

,30 

80 

10 


II 01. 


MEAN  EFFECTIVE  VOLUMES 


'IIIC2. 


100  200 


10  400   500  600  700  800  900  1000 

HEAT  UNITS  ADDED. 
FIG.  190. 


pression  the  same  as  the  ratio  of  volume  after  heating  to  that 
before,  and  the  final  volume  is  proportional  to  Hr  The  constant 
of  proportionality  is  decreased  by  compression  increase. 

8.  The  final  volume  of  Cycle  II  A  is  least  and  equal  to  that 
existing  before  compression. 

9.  When  Hl  is  large  enough  there  may  be  a  value  for  which 
the  final  volume  may  exist  in  the  following  order  of  magnitude: 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  455 

III  Cj,  7000.00;  I  C,  4200.00;  II  C,  2300.00;  III,  75.00;  I, 
65.00;  II,  51.00;  II  A2,  12.38.  A  change  of  compression  by 
which  the  volume  after  compression  is  one  fifth  that  for  the  pre- 
vious case  may  change  this  list  to  the  following:  III  C,  1000.00; 
1C,  4200.00;  IIC,  500.00;  III,4o.oo;  1,65.00;  11,34.00;  II  A2> 
12.38. 

10.  The  mean  effective  volumes  increase  with  Hl  for  all  cycles 
except  II  A2,  in  which  this  variable  is  constant. 

11.  For  Cycle  III  the  M.E.V.  is  proportional  to  Hv  and 
increase  of  compression  increases  the  constant  of  proportionality. 

198.  Comparison  of  Cycles  with  Respect  to  Heat  Discharged 
or  Abstracted.  Work  Done.  Efficiencies. — A  comparison  of 
the  several  cycles  from  this  point  of  view  leads  at  once  to  the 
deduction  concerning  their  relative  efficiency.  Plotting  the 
curves  from  the  following  equations : 

Cycle. 

I.  H2  =  CpTa(X7-!), (50) 

/  TT    \ 

I/"""*  TT  T*      X"*t         1  ~\7~  T\     /~*    1  /  t  J-J-  1          \  *  * 

c.  H2=r0c,  iog,x=racviog^i+^rj,  .  .   (51) 


1 


II.  H,-C,r.(Xr-i) (52) 

II  A,.  Ht-C,Ta(X^i)-^-u     .......    (53) 


IIC.  ff.-C.rjog^i-gny (S4) 

III.  H,-C,Ta(Y-i)-jj±, (55) 


m/~1  7-7-  /-~i     rri    i  I  -LJ-  1       \  t      s\ 

C.  H2  =  CPTa\og  ( i  +  ,      .       .....     (56) 

3<?\       CPTb)' 

ffi 


IVC.  H^^, (Sg. 

the  following  curves  result. 


4S6 

400 
350 
300 

250 

THE  GAS  ENGINE. 

/ 

WO 

\ 

RK  DO 
Sycle  I 

NE 

/ 

ID 

X 

00 

> 

200 
150 
100 
50 
0 

z 

UJ 

x 

z 

8 

cc 

x 

X 

x 

7 

/ 

100    200    300    400    500    600    TOO    800    9GO    1,000 

HEAT  UNITS  ADDED. 
FIG.  192. 


ouu 

X 

/ 

W^RK  DONE 
Cycle  I  C 

/X 

. 

1 

f- 

CQ 

z 

X 

4DO 

m 

V 

z 

§ 

300 

oc 

jX 

X 

X 

"100 

/ 

il 

r/ 

0     100    200    800    400    500    600    700    800     900    1,000 

HEAT  UNITS  ADDED.     ' 


FIG.  193. 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  457 


WORK  DONE 


ycle  I 


IPO          200 


-400  500  600  700          800          900          1, 

HEAT  UNITS  ADDED. 
FIG.  194. 


WOjRK  DONE 
Jycle  II  A2;  III;  IV  0 


100          800 


400          500          600          700          800          900         1,000 
HEAT  UNITS  ADDED. 

FIG.  195. 


458 


THE  GAS-ENGINE. 


900 


800 


700 


GOO 


500 


400 


100          a00 


600          700          800          900         1,000 

HEAT  UNITS  ADDED. 
FIG.  196. 


WORK  DONE 
Cycle  HI 


100 


0  100  800  300  400  500  600  TOO 

HEAT  UNITS  ADDED. 

FIG.  197. 


900          1,000 


THEORETICAL  ANALYSIS  OF   THE   GAS-ENGINE. 

2.00 


459 


L50 


1.00 


ISO 


i.od 


.50 


WORK  DONE 
Cycle  IV 


100  ^00  300  400 

HEAT  UNITS  ADDED. 


FIG.  198. 


§00 


EFFIC 
Cyc 


ENCY 
lei 


1.50 


1.00 


100 


gOO 


300 


400  500  600 

HEAT  U\JTS  DADOED. 


FIG.  199. 


800 


900 


1,000 


-400  500  600 

HEAT  UNITS  ADDED,. 

FIG.  200. 


700 


800 


900 


1,000 


1.50 
1.00 
.50 

> 

EFFIC 
Cyc 

ENCY 
ell 

z 

UJ 

o 

COMP 

CESSION 

10:1 

HT 

SESSION. 

2-1 

0             100           200           300           400           500         '600           700           800           900         1,00 

HEAT  UNITS  ADDED. 

FIG.  201. 


460 

1.50 


THE   GAS-ENGINE. 


1.00 


1.50 


LOO 


.50 


EFFICIENCY 
Cycle  II  C 


COMPRESSION   10:1 
lESSlQN.Z'-"'' 


300  400  500  600 

HEAT  UNITS  ADDED. 
FlG.  202. 


700          800  900         1,000 


> 

1  EFFICIENCY 
Cydle  II  A|;  HI;  I 

PC 

0 

-z. 

LLl 

COMPRE! 

5SION  10 

1 

U. 

LU 

COMPRESSION  2:1 

0  100  200  300  400  500  600  700  800  900         1,000 

HE'AT  UNITS  ADDED. 


1.50 


FIG.  203. 


"0     100    200     300    400     ,500    600     700    800    900    1,000 

HEAT  UNITS  ADDED. 
FIG.  204. 

1.50 


300  400 

HEAT  UNITS  ADDED. 


FIG.  205. 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  45l 

The  work  done  in  the  various  cycles  in  B.T.U.  is  shown  by 
Figs.  192  to  198,  and  the  efficiencies  in  Figs.  199  to  205. 

Equations  (53),  (55),  and  (58)  are  identical,  that  is,  these  three 
cycles  will  discharge  the  same  amount  of  heat  and  have  the  same 
efficiency;  moreover,  this  efficiency  will  be  independent  of  every- 
thing but  the  compression.  These  three  cycles  have,  further, 
a  common  property  not  seen  by  the  formula,  but  from  their  defini- 
tions each  receives  and  discharges  all  its  heat  according  to  the 
same  law. 

Cycle  II  A  receives  all  heat  at  constant  volume  and  discharges 
all  at  constant  volume. 

Cycle  III  receives  all  heat  at  constant  pressure  and  discharges 
all  at  constant  pressure. 

Cycle  IV  C  receives  all  heat  at  constant  temperature  and  dis- 
charges all  at  constant  temperature. 

A  consideration  of  the  above  would  seem  to  warrant  the  prop- 
osition: 

When  all  the  heat  is  discharged  according  to  the  same  law 
under  which  it  was  received,  then  the  cycle  will  have  an  efficiency 
independent  of  everything  but  the  previous  compression  and  will 
be  given  by 

E=i-    " 


•r-i* 


We  may  remark  here  that  as  IV  C  is  the  Carnot  Cycle  we  can 
state  that  Cycles  II  A2  and  III  have  the  same  efficiency  as  the 
Carnot  Cycle  with  same  previous  compression.  This  is  an  impor- 
tant supplementary  to  the  old  theorem  that  the  Carnot  Cycle  has 
the  highest  efficiency  for  its  temperature  range. 

The  relation  between  the  other  values  of  H2  are  best  shown 
by  the  curves  of  Figs.  199  to  205  by  implication. 

The  following  comparisons  will  be  interesting  and  useful: 
6.  For  Cycles  II  A2,  III,  IV  C  the  efficiency  is  a  function  of 
the  adiabatic  compression  only  and  the  same  function  for  each. 


462  THE   GAS-ENGINE. 

It  is  independent  of  the  amount  of  heat  supplied,  i.e.,  is  not  a 
function  of  H. 

7.  For  all  cycles  the  efficiency  increases  with  the  compression, 
but  not  according  to  the  same  law. 

8.  For  Cycles  IV,  IV  A,   IV  B  the  efficiency  decreases  with 
increase  of  heat  added  to  the  same  mass  of  gas. 

9.  For  all  other  cycles  except  II  A2,  III,  IV  C  the  efficiency 
increases  with  Hlt  but  according  to  different  laws,  so  that  the  dis- 
tance between  efficiency  curves  will  vary. 

10.  For  these  cases  a  change  in  H±  will  produce  more  effect 
when  HI  is  small  than  when  it  is  large. 

1 1 .  After  heat  has  been  added  the  efficiency  will  vary  with  the 
degree  of  expansion.     Cycle  II,  therefore,  will  have  an  efficiency 
always  higher  than  II  A  and  lower  than  II  B  or  II  C. 

12.  Cycles  in  which  an  adiabatic  compression  precedes  heat- 
ing will  always  have  a  higher  efficiency  than  those  lacking  this 
compression,  other  things  being  equal. 

13.  For  the  same  initial  conditions  and  same  heat  added,  if  Ht 
is  large  enough  Cycle  II  C  will  always  have  the  highest  efficiency, 

(  II  A 


and  then  come  in  order  III  C ;  1C;  II  -<  III      >  ,  always   remem- 

five  } 

bering  that  IV,  IV  A,  IV  B,  IV  C  cannot  exist  if  H,  be  large. 

14.  The  difference  in  efficiency  between  the  curtailed  expan- 
sion of  Cycle  II  A2  and  that  of  II  increases  with  the  amount  of 
heat,  the  difference  being  small  when  H x  is  small,  and  greater  as 
HI  increases,  the  greatest  possible  being  about  12  per  cent. 

15.  Expanding  Cycle  II  to  original  temperature,  making  Cycle 
II  C,  may  increase  the  efficiency  from  5  to  15  per  cent  approxi- 
mately for  possible  values  of  Hv 

1 6.  Cycle  III  may  add  by  expansion  to  original  temperature  as 
much  as  25  per  cent  to  the  efficiency  for  possible  values  of  H^ 

17.  Cycles  IV,  IV  A,  IV  B  have  an  efficiency  decreasing  with 
increase  of  H  provided  H  remain  small;  when  H  passes  a  cer- 
tain limit  the  cycle  ceases  to  be  possible. 


THEORETICAL  ANALYSIS  OF   THE   GAS-ENGINE.  463 

t8.  A  change  in  the  volume  ratio  of  compression  from  \  to  yV 
vriil  increase  the  efficiency  of  the  cycles  as  follows  for  possible 
values  of  H± : 
Cycle  II 30-20  per  cent  approximately,  depending  on  Hr 

'"     II  A,) 

"     III     > 35  per  cent  approximately,  depending  on  Hr 

"     IV  C  ) 

"     II  C 40-5  per  cent  approximately,  depending  on  Hr 

199.  General  Conclusions  from  the  Analysis  of  Cycles. — Cer- 
tain useful  general  conclusions  may  be  drawn  from  the  fore- 
going analysis,  beside  the  specific  ones  referred  to  under  their 
appropriate  titles: 

If  the  cycle  consists  of  .a  series  of  operations,  or  pressure- volume- 
temperature  changes  resulting  in  a  return  to  the  original  state  of 
pressure,  volume,  and  temperature,  then : 

1.  The  P.V.T.  at  any  point  of  a  cycle  depends  on:    (a)  The 
cycle  itself  qualitatively  considered,  i.e.,  the  nature  and  order  of 
succession  of  the  processes  or  phases  already  completed;    (b)  the 
extent  or  intensity  of  each  phase  of  the  cycle  quantitatively ;   (c)  the 
amount  of  heat,  H,  added  before  reaching  the  point  considered. 
For  example,  the  temperature  at  the  end  of  combustion  will  be 
different  for  different  cycles,  and  will  vary  with  the  compression 
before  heating,  the  law  of  compression,  and  the  amount  of  heat 
added. 

2.  The  part  of  the  total  heat  transformed  into  work  is  a  func- 
tion of  the  cycle,  and  will  vary  with  the  order,  nature,  and  extent 
of  the  cyclic  phases,  except  when  all  the  heat  is  added  and  all 
abstracted  according  to  the  same  law. 

3.  When  the  laws  of  heating  and  of  cooling  are  identical,  then 
the  part  of  the  total  heat  supplied  which  becomes  transformed  into 
work  is  constant  for  the  same  previous  compression,  and  this 
resulting  efficiency  is  a  function  of  the  previous  compression  only 
when  these  other  two  phases,  compression  and  expansion,  com- 
pleting the  cycle,  have  likewise  the  same  law. 

4.  The  range  of  changes  in  pressure,  volume,  and  temperature 


464  THE   GAS-ENGINE. 

is  different  for  different  cycles,  and  in  any  one  cycle  will  depend 
on  the  amount  of  heat  added. 

5.  While  the  variations  noted  do  in  general  hold,  yet  in  the 
different  cycles  each  variable  may  be  a  different  function  of  Hly 
so  that  two  or  more  curves  may  intersect,  and  for  that  particular 
value  of  Hl  the  variable  will  have  the  same  value  in  two  or  more 
different  cycles  simultaneously. 

From  the  data  here  set  down  the  selection  of  a  cycle  on  purely 
ideal  grounds  can  be  made  with  a  full  knowledge  cf  all  the  con- 
ditions surrounding  the  selection;  that  is,  knowing  what  results  are 
desired,  the  cycle  which,  theoretically,  ideally,  cr  mathematically 
considered,  gives  the  results  can  be  found,  and  in  addition  it  is  easy 
to  see  what  accompanying  circumstances  are  inevitable.  If  that 
cycle  which  transforms  the  greatest  amount  of  heat  into  work  ideally 
is  wanted,  it  is  readily  seen  that  II  C  with  as  high  compression  as 
possible  must  be  selected,  but  it  is  also  evident  that  a  very  large 
volume  range  must  be  submitted  to.  If  that  cycle  with  the  lowest 
temperature  range  is  wanted,  then  any  of  Group  IV  must  be  taken. 

If  a  cycle  is  desired  which  will  convert  of  any  amount  of  heat  the 
same  proportion  into  work,  then  any  one  of  II  A,  III,  or  IV  C  may 
be  chosen,  but  of  these  one  has  the  lowest  pressure  range,  another 
the  lowest  temperature  range,  and  the  last  the  lowest  volume  range. 

For  example,  it  is  from  a  comparison  such  as  this  that  the  fol- 
lowing suggestions  are  derived : 

(A)  Cycle  I  and  its  variations,  by  reason  of  its  poor  shewing 
in  efficiency  and  mean  effective  pressure  as  compared  with  the 
previous-compression  Cycle  II,  must  be  set  aside. 

(B)  The  atmospheric  cycles,  by  reason  of  their  low  mean 
effective  pressure  and  consequent  large  volume  range,  are  useless 
for  power  purposes  as  compared  with  the  other  cycles. 

(C)  This  leaves  as  the  only  cycles  worthy  of  application  II, 
III,  IV,  and  their  variations. 

(D)  Of  the  last  mentioned,   the  three  which  are  peculiar, 
Cycle  II A2,  Otto,  heating  and  cooling  the  gas  at  constant  volume; 
Cycle  III,  Bray  ton,  heating  and  cooling  the  gas  at  constant  pres- 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  465 

sure ;  and  Cycle  IV  C,  Carnot,  heating  and  cooling  the  gas  at  con- 
stant temperature,  have  the  same  efficiency  for  the  same  compres- 
sion, and  should  consequently,  with  the  same  heat  supplied,  do 
the  same  work. 

The  efficiency  of  each  is  given  by 

:        .  *-'-(£)'":  WiMiJi- 

where  Va  is  the  volume  before  compression, 
Vb  "    "        "        after 
f    "    "    ratio  of  specific  heats,  and  for  air  f=  1.406. 

(E)  The  other  cycles,  II,  II  B  and  C;  III  A  and  B;  IV,  IV  A 
and  B,  can  easily  be  given  their  proper  comparative  position  by 
remembering  that  each  is  a  more  or  less  complete  expansion  of  one 
of  the  above  three.     For  example,  if  in  the  Otto  the  expansion 
were  carried  to  atmospheric  pressure,  the  efficiency  would  be 
greater  than  for  the   Otto.     Similarly  with  the  Carnot,   if  the 
expansion  were  stopped  at  atmospheric  pressure,  as  was  first  sug- 
gested by  Diesel,  the  resulting  Cycle  IV  would  have  an  efficiency 
less  than  the  Carnot,  and  hence  less  than  either  the  Otto  or  Bray- 
ton cycles. 

(F)  If,  as  respects  the  other  variables  entering  each  of  the 
cycles  adopted  for  comparison,  there  be  assumed 

C  mass  of  gas, 
The  same-J  heat  supplied  after, 

1^  compression, 
there  will  result  for 

Cycle  II  A,  Otto,        ) 

«     rrr     TJ  same  work  done,  and  hence  same 

"     III,    Bravton,  >        „  . 

«     IVC.Camot,    j       efficlency- 
And,  further, 

Lowest.  Intertnsdiate.  Highest 

Maximum  temperature Carnot  Brayton  Otto 

Pressure  range Brayton  Carnot  Otto 

Volume  range Otto  Brayton  Carnot 

Temperature  range Carnot  Brayton  Otto 

Mean  effective  pressure. Carnot  Brayton  Otto 

Pressure  range  ^  /v-f^ 

— & Brayton  Carnot  Utto 

Mean  effective  pressure 

Mean  effective  temperature.  . . .     Carnot  Brayton  Otto 


466  THE  G4S-ENGINE. 

The  relation  of  the  Diesel  to  the  Otto  and  Brayton  is  easily 
seen  if  it  be  recalled  that  it  is  an  imperfect  Carnot. 

11.  Some  of  these  variables  should  be  a  maximum  and  some 
a  minimum.     For  the  maximum  temperature  the  Carnot  holds 
first  place,  but  its  impracticability  yields  the  place  to  Brayton. 
Neither  pressure  range  nor  mean  effective  pressure  is  wanted  by 
itself,  but  only  the  ratio  between  them,  for  it  is  to  this  ratio  that 
the  weight  of  the  engine  must  be  approximately  proportional; 
here  Brayton  holds  the  most  favorable  place. 

Volume  range  should  be  low,  and  here  first  place  is  held  by 
the  Otto.  The  mean  effective  temperature  should  be  low,  and 
the  Brayton  is  exceeded  only  by  the  Carnot. 

The  low  mean  effective  pressure  of  the  Carnot,  and  all  other 
isothermal  combustion  cycles,  is  sufficient  warrant  for  cutting 
them  out  of  consideration  in  comparison  with  the  Cycles  II,  III, 
and  their  variations. 

The  conclusion  is  thus  reached  that,  theoretically,  the  last- 
named  cycles  only  are  worthy  of  further  consideration.  , 

12.  In  the  above,  the  hypothesis  that  heat  could  be  added  to 
the  gas  has  been  assumed,  and  no  account  taken  of  the  means  of 
so  doing,  but  this  point  needs  consideration.     If  heat  be  added 
through  walls  from  a  source  of  known  supply,  of  which  we  can 
control  and  use  as  much  or  as  little  as  we  please,  there  will  be  no 
alteration  in  the  formulae  or  results  of  the  analytical. comparison; 
but  the  internal-combustion  method  of  heating  presents  some 
new  questions  for  solution.     First,  the  air  and  fuel  become  car- 
bonic acid,  steam,  etc.,  and  as  to  what  value  of  the  specific  heat 
should  be  used,  who  can  say?     (Par.  55.)    Second,  the  chemical 
change  is    accompanied   by  an  intrinsic  volume   change.     (Par. 
14.)    Third,  there  may  be  reasons  why  the  fuel  should  give  out 
more   heat   when   burned   in    one   way   than   when  burned    in 
another. 

13.  The  only  ways  of  heating  by  internal  combustion  which  are 
worth  anything  for  power  are  the  constant- volume  and  constant- 
pressure  methods.      On  theoretical  grounds  there  is  no  reason 


THEORETICAL   ANALYSIS  OF  THE   GAS-ENGINE.  467 

for  saying  that,  for  any  particular  system  of  combustion,  more 
heat  can  be  developed  one  way  than  the  other.  The  evidence 
that  heat  has  been  added  to  a  mass  of  gas  in  an  engine  is,  for  the 
two  cases,  (A)  an  increase  of  pressure,  and  (B)  an  increase  of 
volume.  This  pressure  increase  on  the  one  hand  and  volume 
increase  on  the  other  can  be  readily  observed  by  indicators,  and 
the  results  of  these  observations  on  a  large  number  of  indicator- 
cards  show  that  the  increase  is  not  what  it  should  be  if  all  the 
calorific  value  of  the  fuel  had  developed. 

In  short,  there  is  in  practice  abundant  evidence  of  heat  suppres- 
sion, and  whether  this  be  due  to  radiation,  conduction,  dissocia- 
tion, or  an  increase  of  specific  heat,  or  to  an  actual  non-production 
of  heat  is  unknown.  What  is  known  and  can  be  asserted  is  that 
the  effects  on  pressure  and  volume  are  such  as  they  would  be  if 
only  a  part  of  the  heat  supposed  to  be  generated  had  appeared. 
The  result  might  be  worked  up  to  give  a  new  value  to  the  heating 
power  of  the  fuel,  to  be  called  its  effective  calorific  value,  or  a  new 
value  given  to  the  specific  heat,  to  be  called  the  effective  specific 
heat  of  the  process. 

14.  For  constant- volume  combustion  the  value  for  Hly  the 
British  thermal  units  per  pound  of  mixture,  will  be  derived  from 
the  equation 


•*  * f T    I  V 

A   r,     hc.2V 

where  ^t  =  pressure  before  compression ; 

I\  =  temperature  before  combustion; 
p2  =  pressure  after  combustion; 
T2  =  temperature  after  combustion; 
Cv  =  specific  heat  at  constant  volume. 

This  ratio  in  the  general  run  of  gas-engines  will  average  about 
3.5.  In  some  cases  it  may  reach  4,  but  it  seldom  has  reached 
6.  Some  values  are  given  below: 


468  THE  GAS  ENGINE. 

Engine.  -~  Remarks 

Pi 

Westinghouse 3  On  gas 

Otto 4.5. N.  Y.  gas 

Hornsby- Ackroyd 3.5  Kerosene 

Nash 4  N.  Y.  gas 

Clerk 4  Glasgow  gas 

Crossley 3  Dowson  gas 

Priestman 3.5  Kerosene 

Crossley  oil 3.5  Kerosene 

A  general  statement,  very  nearly  true,  would  give  these  pres- 
sure and  temperature  ratios  about  50  per  cent  of  what  the  usual 
values  of  H^  and  Cv  would  produce.  These  figures,  while  not 
strictly  true  for  any  one  case,  give  a  fair  average  value. 

15.  The  other  system  of  combustion — that  at  constant  pres- 
sure— may  be  observed  in  the  same  way.  The  only  indicator- 
card  available  from  this  type  of  engine  was  taken  from  a  Bray  ton 
oil-engine  with  its  smoky  fire.  The  volume  ratio,  in  this  case,  is 
quite  well  given  by  the  relative  lengths  of  the  delivery  line  of  the 
compressor  and  the  admission  line  of  the  power  cylinder,  and  is 
given  by 

^2 

.          >;-:,•      IT3'2'      I  -;       | 

To  compare  this  with  the  pressure  ratios  given.    Theoretically, 

li-T*-         g. 
vi     T,       fC,2Y 

where  CP  is  the  specific  heat  at  constant  pressure  and  the  other 
symbols  are  as  heretofore;  combining  this  with  the  similar  one 
for  the  other  type,  we  get 


or 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  469 

Take  r=I-4>  and 

ir1-4?-4-   y;  '  ;v 

By  substitution,  when 

— =i,      then     —  =i; 

liB  i-  ••  *~«  : 


16.  This  shows  that  when  a  Brayton  engine  gives  a  volume 
ratio  in  combustion  of  3.2  there  is  evidence  of  as  much  heat  as 
would  cause  a  pressure  ratio  of  4.44  in  an  explosion  engine ;  hence 
it  would  seem  that,  for  the  combustion  process  alone,  the  Brayton 
engine,  even  with  its  poor  fire,  was  giving  evidence  of  as  much  heat 
as  the  very  best  explosion  engine,  and  more  than  can  most  of 
them.  This  point  is  very  striking,  and,  in  order  to  verify  or  dis- 
prove it,  a  large  mass  of  data  is  necessary,  which  can  be  collected 
only  after  considerable  time. 

The  above  point  bears  strongly  on  the  formulae  of  cyclic  com- 
parison. The  analysis  showed  that  the  Otto  and  Brayton  cycles 
must  have  the  same  efficiency  for  the  same  heat  added;  but  if 
one,  by  reason  of  its  system  of  combustion,  can  take  from  the  fuel 
more  heat  than  the  other,  then  that  one  must  have  the  higher 
efficiency  in  practice,  assuming  equal  subsequent  heat  losses  and 
equal  friction  losses  in  the  mechanism. 

200.  Formula  for  Theoretical  Mean  Effective  Pressure. 
Otto  Cycle. — A  most  serviceable  deduction  can  be  made  from  the 
analysis  of  the  cycle  for  Groups  II  in  which  the  expansion  and 
compression  curves  are  similar  between  two  terminal  verticals 


470 


THE  GAS-ENGINE. 


(Fig.  206).  The  mean  effective  pressure  will  be  the  area  from 
the  diagram  under  the  expansion  curve  diminished  by  the  area 
under  the  compression  curve  and  divided  by  the  length  of  the 
diagram  between  verticals.  From  paragraph  51  the  mean  effect- 


400 


25 


50 


75 


100 


125 


150 


300 


I 

-§  200 
a 

I 

a 

9  100 


Volumes  in.Tenths  of.a  Cubic  Foot 
FlG.  206. 


ive  pressure  will  be  for  the  two  adiabatics  CD  and  AD,  with  the 
same  value  for  n  in  each, 


The  difference  will  be  the  mean  working  pressure  on  the  piston,  or 


n-i       r-i 

Pb       Pc 


i 


But  the  line  pc  —  pb  measures  the  increase  of  pressure  due  to  the 
ignition  of  the  charge,  and  the  ratio  -^  is  the  ratio  of  the  compres- 


THEORETICAL  ANALYSIS  OF  THE  GAS-ENGINE.  471 

sion  pressure  to  the  explosion  pressure  and  must,  therefore,  depend 
on  the  fuel  varying  with  it,  and  having  a  definite  relation  to  the 
calorific  power.  From  paragraphs  14  and  20  it  became  clear 
that  for  a  fuel  of  Q  calorific  power  in  B.T.U.  the  burning  of  y 
pounds  in  x  pounds  of  air  gave  a  temperature  increase  of 


x+y     CvTb' 


If  this  be  divided  by  Tb, 


rr\  , 

B  ut  Tfr  =  -r  ;  whence 
ib     pb 


Substituting  this,  there  results  the  formula  for  M.E.P.  first  sug- 
gested by  Lucke, 


_ 


pb          x+y     CvTb' 


... 

n-i     (x+y)CvTb     r- 

which  should  be  the  mean  effective  pressure  resulting  when  one 
pound  of  a  mixture  having  a  fuel  value  Q  is  compressed  from  a 
volume  Vi  to  a  volume  vf  and  it  is  ignited  and  then  allowed  to 
expand  down  to  the  original  volume  without  losses  in  the  process. 
If  instead  of  weights  as  in  the  foregoing,  it  be  preferred  to  use 
volumes,  so  as  to  make  the  data  of  the  table  in  paragraph  29 
more  immediately  available,  the  formula  for  mean  effective 
pressure  used  in  paragraphs  29  and  40  may  be  used  involving 
the  calorific  value  of  the  mixture  of  fuel  and  air  per  cubic  foot 
taken  into  the  cylinder  in  the  aspiration  stroke.  This  formula  is 


M.E.P.  - 

144 


H    FTabular  Value  com-1 
a  +  i  [puted  in  Par.  152.     J 


472 


THE  GAS-ENGINE. 


The  diagram  in  Fig.  205  is  the  standard  type  reference  diagram 
of  the  Otto  cycle  (pars.  184,  40,  50,  and  152),  using  the  con- 
stants for  air  to  give  quantitative  results.  The  points  A  and  B 
are  found  from  the  data  of  paragraphs  n,  47,  and  152,  and  the 
tabular  values  computed  in  the  table  of  the  latter  paragraph. 
The  length  of  the  vertical  EC  or  the  line  of  ignition  causing 


400 


50 


75 


100 


125 


150 


r§  200 


100 


Vi 

Volumes  in  Tenths  of  a  Cubic  Foot 

FIG.  205. 

increase  of  pressure  and  temperature  at  a  constant  volume  is 
deduced  from  the  data  of  paragraph  46.  If  the  quantity  of  heat 
given  to  one  pound  of  air  by  the  ignition  of  the  fuel  be: 

Ht  =  C,  (T,  -  T3), 
then  by  the  Gay-Lussac-Mariotte  law  (pars.  44,  45): 


whence 


since 


T         T 

•*•  1  ^  3 


P, 


+    I 


T 


=  i  and  — l  -  i  =  —-'• 
*  i  c» 


THEORETICAL  ANALYSIS  OF   THE  GAS-ENGINE.  473 

Multiplying  through  by  ps  it  is  also  true  that 

O|;  J.    g 

But  since 

and  ^  =  778  (Cp  —  Cw) 

t 

V      /p0\n 
and  -pr  =  (j-J 

it  follows  that 

A       778  (Cp  -  C,) 


778  (n  -  i) 
T 

F°  w 


where  the  pressures  are  in  pounds  per  square  foot.     Dividing 
by  144  to  reduce  to  pressures  in  pounds  per  square  inch  and 

substituting  for  •£%?  its  value  **1       ™  it  follows  that 


3V 


But  the  ratio 

HJ  _  B.T.U.  per  pound  of  the  mixture 
V0      Volume  of  mixture  in  cubic  feet 
and  hence 

=  B.T.U.  per  cubic  foot  of  mixture 

which  is  the  quantity  tabulated  in  columns  n  and  12  of  the 

r^- 
table  in  paragraph  29,  and  which  is  there  called  -  if  there  are 

no  neutrals  present.     When  neutrals  are  presented  to  dilute  the 


474  THE  GAS-ENGINE. 

mixture  the  quotient  should  be  less  heat  per  cubic  foot,  or  the 

TT 

denominator  should  be  •     Substituting  this,  the  pres- 

n  +  a  +  i 

sure  rise  from  ignition  should  be 

P.-P.-2.21\-    — Ix-i, 

In  +  a  +  ij      //.A-1 

W       .  (pj 

If  there  is  no  compression  of  the  mixture  so  that  —  is  unity  the 

rise  of  temperature  is  less  as  has  been  elsewhere  established. 

If  the  volume  of  neutrals  be  taken  as  filling  the  clearance  vol- 
ume completely  and  at  the  temperature  (62°  F.)  of  the  incoming 
mixture  to  eliminate  the  temperature  factor,  no  essential  error 
will  be  made.  In  this  case  n  will  be  N  =  Vy,  and 

N  V3 

<TT7 ==  v,  -  vf 

whence 

2.21  H 


.     .7! 


\          a        /  .  x 

m] 

w 

In  this  by  substituting  for  -  f—  its  equivalent  i  —   ( 

v,  ~  »/ 
the  expression  becomes 


.71. 


-          -   2.21 


in  which  the  tabular  values  may  be  substituted  from  paragraphs 
29  a*hd  152.  When  the  position  of  the  point  C  is  thus  found 
the  location  of  the  theoretical  expansion  line  is  fixed  and  the 
curve  drawn  by  the  relation  pxv^Al  =  #ttywl  in  which  the 
second  member  is  given,  and  each  pressure  found  by  dividing 
this  quantity  by  the  assumed  volume.  Such  a  standard  diagram 
can  then  be  taken  as  a  standard  or  as  unity  of  possible  per- 
formance. The  actual  performance  will  be  some  fraction  of 


THEORETICAL   ANALYSIS  OF  THE  GAS  ENGINE.  475 

the  possible  air-card  standard;  or  the  air-card  area  or  performance 
should  be  multiplied  by  a  factor  less  than  unity,  to  give  the  actual 
performance.  Such  a  multiplier  may  be  called  as  in  steam- 
engine  design,  the  "  diagram  factor,"  and  some  values  for  it  will 
be  given  in  the  next  paragraph  after  investigating  the  causes 
which  increase  the  size  of  its  denominator. 

If  the  first  formula  above  for  M.E.P.  be  applied  to  an  example 
with  the  following  data: 

ra  =  62°  F. +460-522°; 

pa=i4.j  Ibs.  per  sq.  inch  or  2116.4  per  sq.  foot; 

i  cu.  ft.  gas  weighing  .032  Ibs.; 

i  cu.  ft.  air  weighing  .078  Ibs., 

so  that  5.6  cubic  feet  of  air,  the  best  volume  for  one  volume  of 
gas  weighs  .437  pound,  and  6.6  cubic  feet  of  the  mixture  will 
weigh  .43 7 +  .03 2  =0.469  pound,  whence  i  cubic  foot  of  the 

mixture  will  weigh  '     ,    =.071  pound,  or  the  volume  of  one 

pound  of  the  mixture  va=i4  cubic  feet.  Let  the  value  for  n  be 
taken  the  same  as  for  air  1.4,  Cv= 0.1689,  and  suppose  the  ratio 

Vn 

-  =  5.     Then 

,  per  sq.  ft. 

=  14.7  X  9.5  =  140  Ibs.  per  s 

n- 


A*(5)1'4==2ii6.4X9.5  =  2o,io61bs.  per  s 
=  14.7X9.5  =  140^5.  per  sq.  in.; 

ra(5)'4=  522  X  1.9-992°  absolute; 
i  =      .4  = 


yQ 

For  this  gas =  1 600 ;  whence 


If  the  specific  heat  be  taken  as  that  for  a  composition  of  the 
products  of  combustion  made  up  of  one- third  CO2  and  the  rest 
steam-gas,  the  M.E.P.  will  be  less  as  this  greater  value  for  the 
specific  heat  comes  in  the  denominator.  Or  again,  if  the  experi- 


476  THE  GAS-ENGINE. 

mental  or  effective  values  for  the  specific  heat  be  taken  as  given 
in  paragraph  55,  then  the  M.E.P.  comes  lower,  or  a  little  over 
100  pounds  per  square  inch,  which,  while  still  higher  than  prac- 
tice values,  is  much  nearer  than  the  computation  above  will  give. 
What  are  the  factors  explaining  this  loss  of  heat  ? 

20 1.  Factors  Reducing  Computed  Mean  Effective  Pressure. — 
Diagram  Factor. — Some  of  these  have  been  already  referred  to  in 
other  connections,  but  are  here  recapitulated  and  supplemented. 

1.  The  pressure  in  the  cylinder  at  the  time  when  the  volume 
is  va  is  not  that  of  the  atmosphere,  but  is  below  it.     Hence  the 
full  weight  of  the  mixture  is  not  really  present.     The  causes  for 
this  diminished  weight  include: 

(a)  Friction  in  the  suction  valve  and  the  piping  and  passages, 
if  tortuous  or  small. 

(b)  The  delay  in  opening  of  the  valve  if  an  automatically  lift- 
ing one.     It  will  not  open  until  the  pressure  on  top  is  below  that 
underneath  it. 

(c)  The  inertia  of  the  valve  and  of  the  column  of  air  and  fuel 
outside  the  valve. 

2.  Loss  of  weight  in  the  charge  by  heating  as  it  enters  while 
the  valve  is  still  open  to  atmospheric  pressure.     This  heating 
may  be  effected  by  the  hot  metal,  or  by  the  hot  products  of  com- 
bustion  trapped   in   the   clearance   volume.     High   compression 
and  lessened  clearance  volume  diminish  this  loss. 

3.  The  compression  may  be  nearer  isothermal  than  adiabatic 
by  reason  of  low  jacket  temperature  taking  off  heat  in  compression 
and  lowering  the  value  of  _/>&.     This  loss  will  be  less  with  hot 
jacket  water  and  at  high  speeds  of   the  piston,  but  the  hotter 
walls  will  increase  the  loss  in  No.  2. 

4.  The  ignition  line  instead  of  being  vertical  may  be  inclined 
by  a  retarding  of  the  time  of  firing  the  charge.     Compare  the  dis- 
cussion of  governing  by  ignition  in  paragraph  115.    The  indicator- 
diagram  with  retarded  ignition  (Figs.  86  and  87)  shows  a  lower 
pressure  at  its  maximum  point  because  the  mixture  had  partly 
lost  its  compression  pressure  before  it  was  ignited. 


THEORETICAL  ANALYSIS  OF  THE   GAS-ENGINE.  477 

5.  The  presence  of  diluent  neutral  gases  from  a  previous 
stroke,  or  an  impoverished  or  excessively  rich  mixture,  will  delay 
the  propagation  of  the  flame  in  the  mixture,  increasing  loss  No.  4. 

6.  The   degree   of  the   compression   before   explosion.     The 
higher  the  compression  pressure  the  higher  the  value  for  pc  when 
other  things  are  equal.     But  the  qualities  of  the  fuel  cannot  be 
disregarded  here  with  respect  to  the  temperatures  at  which  the 
heat  caused  by  compression  will  cause  them  to  ignite,  perhaps 
before  the  completion  of  the  compression. stroke.     With  common 
illuminating-gas  from  coal  or  with  gasoline  a  compression  to  90 
pounds  or  6  atmospheres  should  not  be  exceeded;   with  kerosene 
vapor  the  ignition  or  pressure  limit  is  at  3^  to  4  atmospheres 
with  hot  cylinder- walls,  while  the  weaker  gases  from  producers 
or  from  blast-furnaces  may  be  compressed  to    15    atmospheres 
without  pre-ignition. 

7.  The  length  of  the  explosion  line  EC  (Fig.  205)  will  be  fixed 
by  the  character  of  the  fuel,  other  things  being  equal.     With  the 
compression  pressure  fa  fixed  by  the  limits  set  in  No.  7  the  ratio 
of  the  explosion  pressure  pc  to  it  will  be: 

-^  for  weak   producer  and   furnace  gas=2; 

"    "    illuminating-  or  coal-gas  =2.5104; 

"    "    natural  gas  and  carbureted  gas  =3104.5; 

"    "    gasoline  =  3  to  5 ; 

j  quite  variable  in  en-  j 

"    "    kerosene  I  gines  using  injection  >  =  3  to  6. 


and  other  systems 


The  ratio  can  be  made  anything  less  than  this  by  incomplete 
combustion  from  any  cause.  For  instance,  gas-  or  gasoline-engines 
which  should  normally  give  a  ratio  of  4  can  easily  be  brought 
down  to  an  actual  relation  of  1.5,  as  revealed  by  applying  an 
indicator. 

8.  The  expansion  line  may  have  its  pressure  ordinates  lowered 
by  conduction  of  heat  to  the  walls  and  jacket. 


478  THE   G4S-ENGINE 

9.  The  exhaust-valve  is  almost  universally  made  to  lead  the 
piston  slightly  so  as  to  open  before  the  stroke  ends  and  relieve 
the  resistance  against  the  return  or  exhausting  stroke  from  the 
very  start.     This  causes  a  loss  of  work  area  to  the  diagram. 

10.  The  exhaust  stroke  should  be  made  against  atmospheric 
pressure  only.    When  the  exhaust  area  is  small  at  the  valve  or  in  the 
passages  an  unnecessary  resistance  acts  like  a  brake  to  diminish 
the  power  of  the  engine.     Mufflers  may  produce  this  effect,  but 
the  loss  here  is  not  so  much  the  direct  consumption  of  power  as 
it  is  the  effect  produced  on  the  succeeding  charge  as  treated  in  loss 
No.  5. 

These  causes  of  loss  are  of  importance  not  only  in  operating, 
but  as  affecting  design  of  new  work.  The  necessary  disagree- 
ment between  theory  and  practice  at  this  point  opens  a  promising 
field  for  research  and  experiment,  so  as  to  ascertain  for  each 
class  of  engine  the  factor  or  coefficient  by  which  the  theoretical 
mean  effective  pressure  is  to  be  multiplied,  so  that  the  formula 
shall  represent  actual  output  from  assumed  values  of  heat  energy 
supplied.  An  empirical  formula  of  this  sort  (Grover)  makes 

M.E.P.  =  2pb  -  o.oipb\ 

in  which  as  before  pb  is  the  pressure  at  end  of  compression.     (See 
par.  40.) 

It  will  be  plain  in  reviewing  these  occasions  of  loss  that  some 
will  be  inherent  in  the  motor  by  reason  of  lack  of  skill  or  experi- 
ence in  the  designer,  and  others  from  lack  of  these  same 
qualities  in  the  operator.  If  the  valves  are  responsible  for  the 
failure  to  receive  the  full  weight  of  charge,  as  in  No.  i,  it  may  be 
because  they  are : 

(a)  Of  too  small  diameter. 

(b)  Not  caused  to  lift  enough. 

(c)  Fitted  with  too  heavy  or  stiff  a  spring. 

(d)  Fitted  with  badly  designed  cams. 

(e)  Opened  by  cams  improperly  set. 

(/)  Controlled  by  a  governor  poorly  designed,  or  working 
badly  from  lack  of  care. 


THEORETICAL  ANALYSIS   OF   THE   GAS-ENGINE.  479 

Defective  valve  design  or  adjustment  may  also  cause : 

(g)  One  cylinder  with  exhaust  at  high  pressure,  because 
just  beginning,  flowing  back  into  another  just  finish- 
ing its  exhaust  stroke. 
(h)  Excess  of  back-pressure  preventing  the  entry  of  new 

mixture  under  its  low  pressure. 

(i)  In  multiple-cylinder  engines,  as  in  the  motor-car,  the 
shape  of  the  inlet  passages  may  preclude  equable 
distribution  of  fuel  mixture  to  all  of  the  cylinders, 
so  that  some  get  less  than  others.  The  passages  may 
be  tortuous  or  crooked. 

(/)  The  speed  of  the  piston  may  be  too  high  in  relation  to 
areas,  or  for  the  inertia  of  the  mixture  itself  to  be 
overcome  and  permit  motion  of  air  and  fuel. 
But,  granting  the  charge  is  of  full  weight,  the  events  in  the 
cylinder  or  adjustments  of  the  carburetor  may  preclude  the 
charge  getting  its  chance  to  work.  Leakage  past  the  piston  is 
of  all  others  the  most  fatal  of  these  defects.  It  not  only  lowers 
the  mean  effective  pressure  directly,  but  by  the  loss  of  com- 
pression pressure  it  acts  indirectly  also.  Defective  mixture  in 
relation  to  the  piston  speed  and  too  early  release  by  opening  the 
exhaust  prematurely,  add  to  the  effect  of  incorrect  timing  of  the 
ignition.  If  the  breech  end,  or  the  volume  of  the  clearance  for 
combustion  of  the  mixture  is  unskilfully  moulded,  the  ignition 
pressure  possible  for  that  mixture  is  not  reached,  and  the  mean 
pressure  is  less  than  it  might  be  if  the  maximum  is  lowered.  If 
the  charge  is  partial  at  the  outset,  by  reason  of  throttling  or 
governing  action  to  reduce  the  power  of  the  stroke,  the  propor- 
tionate effect  is  increased  and  the  mean  effective  pressure  falls, 
therefore,  faster  in  this  case.  What  allowances  should,  therefore, 
be  made  quantitatively  for  these  actions,  and  what  values  should 
be  given  to  the  diagram  factor?  The  following  table  (Lucke) 
brings  together  some  accepted  comparisons  of  theoretical  air- 
card  values  with  the  observed  values  from  the  actual  card.  The 
average  seems  to  lie  between  50  per  cent  and  65  per  cent,  provided 


480 


THE  GAS-ENGINE. 


the  engine  pistons  and  valves  are  fairly  tight,  and  the  mixture, 
and  ignition  are  properly  adjusted,  and  neither  back-pressure  nor 
suction  throttling  are  present. 

TABLE  OF  VALUES  OF  THE  DIAGRAM  FACTOR.* 


1 

2 

3 

4 

5 

Fuel  used  in  motor. 

Compressive 
Pressure 
Absolute. 

Ratio  of 
Ob.   Pressure 

Range  of  Average 
Compressions 

Range  of 
Average 

< 

Pounds  per 
sq.  in. 

A.  c.  Pressure 

Ratios. 

Gasoline  vapor  

40 

Per  cent 

<c8 

80—  I  7O 

CO—  7O 

<«            « 

7e 

<;6 

Jv    O^ 

"        carburetor  

71? 

4.0 

Kerosene  vapor 

g 

60 

"         injected 

vo 

CQ 

HO    io 

Carbureted  water-gas 

Dw 
OO 

s8 

00 

0" 

CQ 

6o—OO 

4^ 

Coal  gas          

60 

60 

"+3 

IOO 

C2 

80 

4? 

Natural  gas  

lie 

61 

OO—  1  4O 

C2—  4O 

I2O 

CT 

IOO—l6o 

^6—4O 

Blast-furnace  gas 

l84 

re 

I7O—  I  80 

D"    V 

48—7O 

JO 

202.  Design  of  Cylinder  Volumes.  —  The  formula  for  the 
mean  effective  pressure  leads  directly  to  the  choice  of  the  cylinder 
volume  for  a  required  horse-power  to  be  developed.  The 
accepted  formula  for  a  piston  motor  (par.  40)  takes  the  form 

H.P.  ,  U^L, 

33,000 

in  which  for  the  gas-engine  P  is  the  mean  effective  pressure  just 
discussed,  and  N  is  the  number  of  working  strokes  or  ignitions 
occurring  in  one  minute.  The  ratio  of  d,  the  diameter  of  the 

cylinder  (TT—  =  A),  to  the  length  of  the  stroke  L  has  been  gen- 
4 

erally  conceded  to  lie  between  d  =  L  and  L  =  2d.  A  stroke  of 
twice  the  diameter,  however,  which  is  quite  usual  with  other 
media,  is  rarely  encountered  in  small  gas-engine  design,  and 

*  The  diagram  factor  for  two-cycle  power  cylinders  may  be  taken  at  0.8,  that 
of  four-cycle  cylinders  to  which  the  above  table  refers.  The  rate  of  M.E.P. 
increase  seems  to  decrease  as  the  compression  increases. 


THEORETICAL  ANALYSIS  OF   THE   GAS-ENGINE.  481 

preference  seems  to  centre  around  L  =  i.2$d  and  L  =  1.3^. 
With  P  and  N  assumed,  and  L  expressed  in  terms  of  d,  the  equa- 
tion can  be  solved  for  d,  which  will  give  the  piston  displacement. 
For  example,  if  the  piston  speed  be  assumed  to  be  500  feet  per 
minute,  pb  =  So  pounds,  and  5  =  i.$d,  the  computation  for  a 
25-H.P.  engine  will  be 


piston    speed 
R.p.m.  =  -  ---      -  =  -^-F-> 
2  X  stroke         30 

giving  for  an  Otto  cycle, 

R.p.m.       500 

Explosions  per  minute  =  —  -  -  =  ^— 

2  6d 

Using  the  empirical  formula  for  M.E.P., 


=  1  60  —  [o.oi  X  6400] 
=  96  pounds  per  sq.  in. 

Whence,  since  H.P.=  -      - 


or 

D2  =  87.5  about, 
and 

jD  =  9-5  nearly, 
and 

£-9.5X1.5-14+. 

203.  Volume  of  the  Clearance.—  For  the  volume  of  the 
clearance,  the  practice  of  the  present  day  has  settled  upon 
a  ratio  of  initial  to  final  pressures  and  volumes  expressed  by 
the  equation 


when  the  subscripts  a  belong  to  the  state  at  the  beginning  of 


482 


THE   GAS-ENGINE. 


compression,  and  the  subscripts  b  belong  to  the  higher  values 
just  before  ignition.     If  these  be  written 


1.35 


the  compression  pressure  in  the  clearance  is  given  when  the 
initial  pressure  is  known  (usually  the  atmospheric)  and  the  ratio 
of  volumes.  (See  previous  treatment  in  paragraph  152,  from  which 
this  is  repeated.)  Ordinarily,  however,  the  compression  pressure 
limit  is  fixed  by  the  condition  that  pre-ignition  is  not  to  be  caused, 
and  the  formula  will  be  used  in  the  form 


The  usual  compression  values  in  pounds  per  sq.  in.  for  the 
various  kinds  of  gas  are  about  as  follows: 


In  Engines  of 

Blast-fur- 
nace Gas. 

Producer- 
gas. 

Weak 
Ilium.  Gas 

Rich 

Ilium.  Gas 

Natural 
Gas. 

Small  and  medium  sizes 

125 
140 

90 
80 

<>5 
60 

55 
60 

Large  sizes   .  . 

J5° 

Taking  from  this  the  ratio  of  pressures  desired   (probably 
about  4  atmospheres  pressure  for  ordinary  gas  for  fa  will  give 

the  ratio  -7-  =  - )  and  the  ratio  of  the  clearance  volume  to  the 
Pb      4/ 

piston   displacement   follows   directly   when   this   assumption   is 
made.     Hence 

va  =  piston  displacement  +  clearance ; 

(Pa\   *'S5 

Vb  =  [stroke  X  area  +  clearance]  U-rjl       , 
which  can  be  transposed  into 

[lPa\   l'35~]  (Pa\  1>35 

i  —  (-f-J        I  =  [piston  displacement]  (— j      ."^ 

Applying  this  to  the  9^X14  cylinder  of  the  25-H.P.  engine 
schemed  in  the  foregoing  paragraph,  with  80  pounds  compression 


THEORETICAL  ANALYSIS  OF   THE  GAS-ENGINE.  483 

pressure,  and  assuming  the  value  for  pa  to  be  14  pounds,  we  have 

va  =  vb+i4  inches, 

substituting  lengths  for  volumes,  to  which  they  are  proportional 
when  the  area  is  constant  as  in  a  cylinder.     Then 

i4-ya1-3  =  95(i/a-i4)1*3; 
whence 


=  (va- 14) (3-36)  nearly 
=  18.1; 
whence  the  actual  volume  of  the  clearance 

vb=  (18.1-14)  X  — 
4 

=  283  cubic  inches. 

204.  Velocity     through     Valves,     Ports,     and    Passages.— 

The  discussion  in  paragraph  98  indicates  that  considerable 
loss  of  power  both  direct  and  indirect  will  follow  if  the  flow  of 
gas  and  air  through  the  valves  is  made  so  rapid  as  to  entail  exces- 
sive friction.  Such  loss  is  both  of  pressure  and  effective  volume. 
This  trouble  is  worse  with  automatic  than  with  mechanically 
operated  valves.  Present  good  practice  in  small  engines  at  very 
high  speed,  for  automobile  uses,  favors  keeping  the  velocity 
of  inlet  flow  at  or  below  60  lineal  feet  per  second  for  automatic 
valves,  while  permitting  90  feet  per  second  for  mechanically 
lifted  valves.  The  exhaust  flow  out  of  the  cylinder  will  be  rapid 
enough  at  75  feet  per  second. 

205.  Mechanical    Design    of    Gas-engines  Regarded  as  Ma- 
chines.— The  design  of  the  gas-engine  from  the  structural  point 
of  view,  with  respect  to  weight  of  fly-wheel,  diameter  of  shaft, 
bearing  surfaces,  cross- sectional  area  of  parts,  and  the  like,  belongs 
to  a  separate  department  from  that  before  the  student  throughout 
this  treatise.     It  has  also  been  so  well  and  completely  worked 
out  by  others  in  forms  accessible  to  every  one  interested  that  it 
does  not  seem  desirable  to  expand  the  treatment  of  this  section 


484  THE  GAS  ENGINE. 

to  include  it.*  The  gas-engine  as  an  achievement  in  machine 
design  falls  under  the  same  laws  and  principles  which  apply  to 
the  steam-engine,  regard  being  paid  to  the  special  character  of 
the  impulses  originating  in  the  cylinder.  The  foregoing  treat- 
ment has  shown  how  to  arrive  at  the  effort  in  the  cylinder,  and 
the  rest  is  machine  designing  along  lines  of  accepted  general 
practice  in  that  art. 

*  A  most  complete  and  exhaustive  discussion  of  this  topic  will  be  found  in 
"Gas  Engine  Design,"  by  Prof.  Chas.  E.  Lucke,  1905.  Parts  II  and  III,  Forces 
Due  to  Gas  Pressure  and  Inertia,  and  Dimensions  of  Engine  Parts. 


CHAPTER  XVIII. 

INTERNAL-COMBUSTION  ENGINES  WITH  HEATING  AT  CONSTANT 

PRESSURE. 

210.  Introductory. — The  previous  chapters  have  been  con- 
cerned principally  with  the  so-called  explosive  engines,  in  which 
a  mixture  of  fuel  and  air  was  ignited  at  a  constant  volume  with 
a  resulting  increase  in  pressure  which  was  utilized  to  impel  a 
piston.  Such  engines  operate  upon  the  Otto  cycle,  in  its  two- 
stroke  or  four- stroke  form,  and  are  widely  used  and  familiar. 

It  is  quite  possible,  however,  to  burn  the  same  explosive 
mixtures  so  that  the  result  of  heating  them  by  the  ignition 
or  combustion  process  shall  be  an  increase  of  their  volume  at  a 
constant  pressure,  and  if  free  to  expand  against  a  movable  piston, 
such  expansion  of  volume  will  take  place  at  a  constant  pressure 
exerted  on  the  piston  while  the  volume  increase  takes  place. 
This  action  is  that  of  Cycle  III,  and  its  analysis  appears  in  para- 
.  graph  185  et  seq.,  as  attaching  to  the  design  of  the  Bray  ton  engine 
in  America  and  the  Simon  engine  in  England.  One  difficulty  at 
the  time  of  their  first  presentation  was  that  due  to  the  difficulty 
of  handling  explosive  mixtures  with  a  continuous  or  intermittent 
release  of  heat  energy  to  act  in  a  motor.  The  work  of  Charles  E. 
Lucke  on  combustion  of  such  explosive  mixtures  in  motion  has 
removed  this  obstacle,  and  has  brought  this  cycle  within  the  scope 
of  practical  realization  either  in  reciprocating  motors  or  in  those  of 
continuous  type,  such  as  the  gas-turbine  principle  presents.  The 
method  for  securing  such  continuous,  manageable,  and  complete 

485 


486  THE  GAS-ENGINE. 

combustion  and  some  principles  underlying  it  form  the  subject 
of  this  chapter,  together  with  some  forms  of  apparatus  using 
the  principle  of  constant-pressure  heating. 

211.  Lucke  Apparatus  for  Continuous  Combustion  of  Explo- 
sive Mixtures. — Referring  to  the  general  statements  of  paragraph 
10,  let  it  be  assumed  that  a  mass  of  explosive  mixture  is  passing 
through  a  non-conducting  tube  with  a  uniform  velocity  v.  Then, 
if  inflammation  be  started  at  some  point,  the  surface  of  com- 
bustion may  remain  at  rest  or  move  with  or  against  the  current. 
Denote  the  rate  of  propagation  by  r.  Then,  when  v>r,  the 
surface  of  combustion  will  move  with  the  current,  and  if  the  tube 
has  an  end,  the  flame  will  "blow  off"  and  combustion  cease; 
if  v  =  r,  the  surface  of  combustion  will  remain  at  rest,  other  in- 
fluences being  inoperative;  if  v<r,  the  surface  of  combustion 
will  move  back  toward  the  source,  or  "  back-flash." 

Of  course,  a  small  tube  of  heat-conducting  material  will 
exert  considerable  cooling  effect,  but  for  the  present  such  tubes 
need  not  be  considered. 

In  a  practicable  system  of  burning  an  explosive  mixture  con- 
tinuously the  following  are  desiderata: 

I.  "Back-flashing"  must  be.  prevented. 
II.  "Blow-off"  must  be  prevented. 

III.  Combustion  surface  must  be  localized. 

VI.  It  must  remain  localized  for  wide  ranges  of  feed  or  veloc- 
ity of  flow  of  the  mixture. 

V.  The  localization  must  be  unaffected  by  changes  of  tem- 
perature. 

VI.  Large  or  small  quantities  must  be  burned  without  affect- 
ing the  above,  and  the  transition  from  very  small  quantities  to 
very  large,  or  vice  versa,  however  sudden,  should  be  easy. 

The  first  requirement  might  be  accomplished  in  three  ways: 

(a)  By  using  a  long  tube  of  some  conducting  material  and 
so  small  in  diameter  as  to  prevent  the  passage  of  the  flame-cap 
under  any  circumstances. 

(b)  By  using  wire-gauze  screens. 


ENGINES   WITH  HEATING  AT  CONSTANT  PRESSURE.       487 

(c)  By  causing  the  mixture  to  flow  at  some  point  with  a 
velocity  always  greater  than  the  rate  of  propagation. 

The  first  (a)  is  impracticable,  as  it  permits  of  only  small 
quantities  being  burned;  the  second  (b)  will  not  work  when  the 
wire  gauze  gets  hot;  this  leaves  (c),  which  is  practicable,  as  a 
valve  in  a  pipe  will  answer  for  the  necessary  contraction  and 
consequent  increase  of  velocity.  Hence  the  first  requirement 
in  the  desired  method  of  combustion  will  be  the  following:  At 
some  point  before  the  combustion  surface  is  reached  the  velocity 
of  feed  must  be  such  that  v>r. 

Requirement  II  might  be  accomplished  in  three  ways: 

(a)  By  so  reducing  the  velocity  after  passing  the  high-speed 
point  that  at  some  surface  v  =  r. 

(b)  By  suddenly  increasing  the  temperature  of  the  mixture 
so  as  to  increase  the  rate  of  propagation  while  v  remains  con- 
stant ;  or, 

(c)  By  both  reducing  v,  by  spreading  the  current,  and  in- 
creasing r  by  heating. 

All  of  these  ways  are  practicable;  but,  as  a  reduction  of 
velocity  alone  or  a  sufficient  heating  alone  would  not  produce 
the  desired  result  so  wTell  as  both  operating  together,  there  will 
be  introduced  as  the  second  requirement  in  the  desired  method 
the  following:  After  passing  the  point  where  ^>r,  the  velocity 
of  the  mixture  should  be  so  reduced  and  its  temperature  in- 
creased as  to  make  vf=  r'. 

Let  the  mixture  issue  from  an  orifice  into  the  air.  By  properly 
regulating  the  velocity  of  exit,  the  flame- cap  can  be  maintained  at  the 
orifice — the  only  device  successful  for  this  purpose  in  certain  experi- 
ments was  to  cause  water  to  drip  into  the  supply-chamber.  The 
position  of  the  flame- cap  is  so  extremely  sensitive  to  changes  of  flow 
that  all  other  methods  which  were  tried  for  obtaining  a  constant 
velocity  of  exit,  variable  at  will,  failed.  Increase  the  velocity  of  flow 
slightly,  and  the  flame-cap  will  lift  off.  This  may  be  done  until  the 
flame-cap  is  as  much  as  2  inches  (with  illuminating-gas  and  air) 
from  the  orifice  before  extinction  takes  place.  It  would  seem  that 


488  THE   GAS-ENGINE. 

the  impinging  of  the  jet  on  the  atmosphere  should  spread  it  and  so 
reduce  its  velocity,  but  no  appreciable  increase  of  diameter  could 
be  observed.  When  the  cap  is  close  to  the  orifice  it  is  of  a  deep 
blue  color ,  uniform  in  shade  over  the  disk,  and  the  edges  are  sharply 
defined;  \vhereas,  as  it  lifts  off  some  distance,  it  becomes  indis- 
tinct and  unsteady  at  the  edges  until,  at  the  moment  of  extinction, 
it  fades  and  disappears.  When  the  cap  is  away  from  the  orifice, 
while  there  is  no  visible  connection  with  the  source  of  supply, 
there  really  exists  a  column  of  mixture  extending  from  the  orifice 
to  the  cap  and  passing  through  the  atmosphere.  Naturally,  at 
the  surface  of  this  column,  diffusion  will  take  place,  and  the  longer 
the  column  the  greater  will  be  this  diffusion  effect,  thus  affecting 
the  composition  of  the  advancing  column  of  mixture  and  causing 
partial  loss  of  gas.  This  is  the  real  cause  of  extinction. 

From  these  experiments  can  be  drawn  the  conclusion  that 
the  current  cannot  be  sufficiently  reduced  in  velocity  by  issuing 
mto  an  atmosphere  of  lower  pressure  to  prevent  " blow-off" 
before  diffusion  with  the  atmosphere  so  alters  the  character  of 
the  mixture  as  to  cause  extinction  or  loss  of  fuel  by  dilution 
before  reaching  the  surface  of  combustion.  This  calls  for  a 
new  condition  besides  those  noted  in  the  requirements  for  com- 
bustion. The  reduction  of  velocity  of  the  mixture,  after  passing 
the  place  where  v>r,  must  be  accomplished  in  such  a  way  as  to 
prevent  diffusion  with  any  other  gas. 

To  prevent  this  diffusion,  there  naturally  suggests  itself  the 
expedient  of  surrounding  the  issuing  jet  with  a  shield  of  larger 
diameter,  to  still  permit  of  the  desired  expansion.  This  is  shown 
in  Fig.  210,  and  is  essentially  the  same  as  proposed  by  Ladd, 
Schmid,  Beckfeld,  and  others.  The  mixture  must  issue  from 
orifice  a  with  a  velocity  ^0>r;  this  will  prevent  "back-flash." 
If  the  distance  from  a  to  b  is  long  enough  to  allow  the  gas  to  spread 
and  reduce  velocity,  "blow-off"  will  not:  occur  until  Vb>r,  and 
within  these  limits  the  flame-cap  should  remain  within  the  shield. 
A  trial  shows  that  when  (Dia)b  is  but  slightly  larger  than  (Dia)at 
the  feed  velocity  may  be  varied  in  about  the  proportions  noted, 


ENGINES  WITH  HEATING  AT  CONSTANT  PRESSURE.       489 

but  this  means  that  action  is  confined  within  very  narrow  working 
limits.  The  flame-cap  seems  to  lose  its  flat,  volumeless  character 
for  some  reason  not  at  first  clear.  When  (Dia)i  is  much  larger, 
say  four  or  five  times  (Dia)a,  a  slow  increase  of  feed  velocity 
above  r  reveals  the  advancing  flame-cap  just  as  if  the  shield 
were  not  there.  Later  a  slight  spreading  is  noted,  and  then  the 


-  1>  |« 

3 

4 
< 

5 

\-f 

6 

7   8 

2 

a^ 

FIG.  210. 

flame  actually  begins  to  show  volume,  as  if  there  were  no  longer 
an  explosive  mixture  present;  this  heats  up  the  shield.  A  little 
consideration  will  show  this  to  be  due  to  the  diffusion  of  the 
advancing  and  slightly  spreading  column  with  the  products  of 
combustion  within  the  shield,  and  the  high  temperature  of  the 
shield  helps  to  maintain  a  combustion  of  what  is  now  a  diluted 
explosive  mixture  beyond  a  point  where  that  combustion  would 
be  possible  if  cold.  An  increase  of  velocity  will  cause  extinction 
by  "  blow-off." 

Here  the  results  are  somewhat  better  than  in  the  last  case 
without  the  shield.  The  principles  operating,  with  the  results, 
are:  back- flash  prevented  by  sufficiently  great  initial  velocity 
at  a;  a  spreading  to  reduce  velocity,  but  very  slight  and  insuffi- 
cient, as  proved  by  the  narrow  working  limits;  diffusion  is  not 
prevented;  gas  is  partly  heated  before  burning  by  the  shield, 
which  helps  to  continue  combustion.  If  the  advancing  column 
did  increase  in  cross-section  and  decrease  in  velocity  while  ad- 
vancing, successive  possible  positions  of  the  flame-cap  would 
be  as  shown  at  i,  2,  3,  4,  etc.,  of  Fig.  210. 

It  is  obvious  that  at  any  point  between  a  and  7,  such  as  4, 
the  cap  is  surrounded  by  products  of  combustion,  and  the  advanc- 
ing column  of  mixture  is  passing  through  an  atmosphere  chiefly 
composed  of  the  same,  resulting  in  disastrous  diffusion.  This 


49°  THE  GAS-ENGINE. 

at  once  suggests  giving  the  shielding  envelope  the  form  of  a  cone, 
supposing  the  orifice  circular,  so  that  the  flame- cap  at  any  in- 
stant may  entirely  fill  up  the  space  between  the  walls. 

Apparatus  with  this  end  in  view  was  tried  and  gave  some 
•nteresting  results.  Fig.  211  shows  a  cone  of  45  degrees  angle, 
with  a  ^-inch  orifice  such  as  was  used.  The 
velocity  of  feed  was  so  adjusted  as  to  cause 
the  flame-cap  to  advance  slowly  from  a, 
with  the  expectation  stated  above.  The 
flame-caps  at  successive  positions  took  the 
forms  shown  at  the  lines  i,  2,  3,  4,  5,  6,  etc., 
and  finally  " blow-off"  occurred.  Since  the 
only  place  where  the  combustion  surface  can 
remain  at  rest  is  on  a  surface  where  v  =  r, 
and  since,  secondly,  r  is  here  constant,  the  curves  indicating  the 
intersection  of  the  combustion  surfaces  by  meridian  planes  give 
us  graphical  values  of  the  velocity  of  the  advancing  column  of 
mixture.  It  is  seen  that  the  expected  spreading  did  not  take 
place,  and  that  at  any  circular  cross-section  of  the  cone  the 
velocity  was  greatest  at  the  centre,  decreasing  toward  the  edges. 

The  curves  i,  2,  3,  etc.,  are  really  cross-sections  of  successive 
constant- velocity  surfaces  in  the  advancing  column,  and  the 
surface  of  combustion  will  lie  on  that  surface  of  constant-trans- 
mission velocity  where  v  =  r. 

A  constant- velocity  surface  may  be  defined  as  a  surface  at 
every  point  of  which  the  moving  particles  of  gas  have  equal  in- 
stantaneous velocities.  If  these  successive  surfaces  had  remained 
flat  or  nearly  so,  the  proper  sort  of  spreading  of  current  and 
uniform  decrease  of  velocity  would  be  indicated.'  This  gives 
an  accurate  definition  of  how  the  velocity  is  to  be  reduced  after 
passing  the  point  where  v>r.  The  velocity  of  the  advancing 
mixture  must  be  reduced  without  diffusion,  so  as  to  keep  the 
surfaces  of  constant  velocity  of  such  form  that  adjacent  points 
on  any  one  will  be  at  approximately  the  same  distance  from  the 
point  where  spreading  begins.  Reducing  the  angle  of  the  cone, 


ENGINES   WITH  HEATING  AT  CONSTANT  PRESSURE.       491 

while  helping  matters  considerably,  reduces  the  range  of  feed 
velocities  within  impracticable  limits. 

Many  ways  of  bringing  about  the  above  were  tried,  but  only 
one  seemed  pre-eminently  good  both  by  reason  of  its  simplicity 
and  effectiveness,  for  it  fulfils  almost  perfectly  the  requirements 
proposed  for  the  desired  method;  this  is,  to  fill  the  cone  with 
fragments  of  refractory  material,  sucn  as  pottery,  broken  crucibles, 
bits  of  magnesite,  or  any  other  rock  which  will  stand  the  high  tem- 
perature without  fusing.  In  cones  of  60  degrees,  and  with  a 
J-inch  orifice,  pieces  about  f-inch  diameter  seem  to  answer  well 

These  separate  pieces  of  solid  matter  interpose  many  reflect- 
ing surfaces  without  materially  hindering  the  advance  of  the 
mixture,  and  cause  it  to  spread  in  the  way  desired,  keeping  the 
surface  of  combustion  spherical  and  preventing  diffusion.  A 
variation  of  velocity  causes  the  spherical  surface  of  combustion 
to  vary  only  in  diameter,  and  the  limits  of  feed  are  determined 
only  by  the  size  of  the  cone. 

A  cone  of  given  altitude  will  give  the  greatest  range  of  varia- 
tion of  diameter  of  cross-section  when  its  angle  is  180  degrees. 
This  is  a  plane  surface  which,  with  the  orifice  and  broken  rock, 
should  appear  as  in  Fig.  212.  Here  the  surface  of  combustion 


FIG.  212. 


is  approximately  a  hemisphere.    Trial  shows  that  this  arrange- 
ment works  perfectly,  and  the  limits  of  feed  are  determined  only 


492  THE  G/tS-ENGlNE. 

by  the  size  of  the  pile  of  rock  surrounding  the  opening.  A  cone 
of  360  degrees,  or  no  cone  at  all,  suggests  the  surrounding  of 
the  nozzle  by  broken  rock  without  any  enclosing  walls  (Fig.  213). 
This  arrangement  also  works  remarkably  well. 


FIG.  213. 

The  surface  of  combustion  is  here  approximately  a  sphere, 
giving  the  greatest  possible  increase  in  area  of  the  surface  of 
combustion  for  the  distance  travelled  from  the  nozzle. 

•If  d  denote  the  distance  from  the  point  where  spreading 
begins  to  the  surface  of  combustion,  and  51  the  area  of  the  sur- 
face, we  have: 

For  a  cone,  S  =  xd2  tan2  a. 

For  no  walls  (Fig.  213),  Sf  =  4xd2. 

Not  only  is  the  greatest  possible  range  of  action  by  velocity 
reduction  thus  obtained,  enabling  the  greatest  possible  amount 
of  mixture  to  be  burned  in  a  given  volume,  but  this  amount  is 
further  augmented  by  reason  of  the  increase  of  the  rate  of 
propagation  caused  by  the  passage  of  the  mixture  between  the 
hot  fragments.  Hence  both  principles  operate  simultaneously 
toward  the  desired  end. 

Hence  a  method  of  continuously  burning  explosive  mixtures 
of  all  sorts,  whether  in  the  chemical  proportion  or  not,  as  classified 
in  Classes  IV  and  V  of  paragraph,  10  seems  to  have  been  found 
which  fulfils  all  the  conditions  set  down  as  necessary,  and  which 
may  be  stated  as  follows: 


ENGINES   WITH  HEATING   AT  CONSTANT  PRESSURE.        493 

I.  Cause  the  mixture  to  pass  a  point  where  its  velocity  of 
transmission  shall  always  be  greater  than  the  rate  of  propaga- 
tion of  inflammation  through  the  mixture.     This  may  be  done 
by  a  valve  in  the  feed-pipe. 

II.  So  spread  the  current  of  mixture  after  it  passes  this  point 
of   high  velocity  that  surfaces  of  constant-transmission  velocity 
shall  be  of  such  form  as  to  keep  adjacent  points  on  any  one  at 
approximately  the  same  distance  from  the  point  where  spread- 
ing begins.     The  whole  spreading  must  take  place  so  that  the 
advancing  unburned  mixture  cannot  diffuse  with  any  other  gas. 
This  can  be  accomplished  by  surrounding  the  orifice  with  solid 
fragments,     introducing     numerous     reflecting     surfaces     which 
accomplish   the   spreading;     also,   by   the   passage   through   the 
interstices  between  this  solid  matter,  the  mixture  is  heated  and 
the  rate  of  propagation  increased,  making  possible  the  burning 
of  more  mixture  in  unit  volume. 

When  a  chemical  proportion  is  maintained  in  the  mixture, 
all  the  combustion  takes  place  on  the  combustion  surface,  giving 
absolutely  neutral  products  of  combustion;  but  when  an  excess 
of  gas  is  present  within  certain  limits,  all  gas  which  can  find  oxygen 
burns  explosively  between  the  solids,  while  the  excess  acts  merely 
as  a  neutral  diluent  to  be  burned  when  it  meets  an  oxygen  atmos- 
phere later  on.  By  properly  placing  the  oxygen  atmosphere 
to  burn  the  excess  gas,  the  hot  products  can  be  made  either  re- 
ducing or  oxidizing — reducing  after  leaving  the  explosive-com- 
bustion surface  and  before  meeting  the  excess  of  oxygen  in  the 
atmosphere,  oxidizing  after  that  meeting. 

It  might  be  here  noted  that  the  principle  well  known  in  explo- 
sive combustion  at  constant  volume,  and  constantly  operating 
in  the  gas-engine,  that  "to  a  chemical  mixture  of  air  and  gas 
there  may  be  added  large  quantities  of  gas  without  altering  the 
explosive  properties  of  the  mixture,"  is,  by  these  experiments, 
extended.  It  appears  that  in  explosive  combustion  at  constant 
pressure,  or  "  continuous  combustion  of  explosive  mixtures," 
the  same  principle  applies,  and,  though  no  real  proportion  measure- 


494 


THE   GAS-ENGINE. 


ments  have  yet  been  made,  it  seems  to  a  wider  degree.  That  is 
to  say,  mixtures  of  air  and  gas,  with  gas  in  excess  of  the  amount 
the  air  present  can  support,  will  burn  explosively.  The  excess 
gas  present  acts  merely  as  a  neutral  diluent,  such  as  the  nitrogen 
of  the  air.  It  is  a  fact,  also,  that  as  the  solid  fragments  heat  up, 
the  excess  may  be  greater  than  when  they  are  cold. 

212.  Engines  which  have  Operated  with  Constant-pressure 
Heating. — To  carry  out  this  principle  in  the  past,  the  engine 
of  Stephen  Wilcox  in  1865  was  designed.  The  central  burner 
between  the  working  cylinders  receives  gas  centrally  from  the 
feed-pump  G,  and  air  is  delivered  from  the  pump  H  around 
the  gauze  surrounding  the  gas-jet  (Fig.  214).  The  heating  of  the 
air  used  for  combustion,  and  some  additional  air  entering  through 
the  valve  M,  causes  the  expansion  which  produces  the  working 
stroke. 


When  Lne  jet  of  fuel  is  projected  into  the  mass  of  air  to  be 
heated  when  the  latter  is  in  the  cylinder,  the  engine  resembles 
the  Diesel  (1892)  or  the  Gibbs  (1897)  in  form.  In  the  Diesel 
the  air  is  heated  to  the  ignition-point  of  the  fuel  by  the  compression 


ENGINES  WITH  HEATING  AT  CONSTANT  PRESSURE.        495 

of  the  previous  stroke;  in  the  Gibbs  the  air  is  not  heated,  but 
the  gas  is  admitted  after  the  compressed  air  has  expanded  after 
cut-off  to  reach  the  lower  pressure  in  the  gas- reservoir.  The 
gas  then  flows  in  and  is  ignited  electrically  (Fig.  215). 


FIG.  215. 

Explosive  mixtures  burning  without  any  atmosphere  of  air 
around  them  are  the  feature  of  the  Brayton,  the  Reeve,  and  the 
Schmid  and  Beckfeld.  The  Schmid  and  Beckfeld  design  in 
Fig.  216  shows  a  supply  of  gas  entering  through  the  pipe  E  and 


FIG.  216. 

air  through  G,  and  mixing  in  the  nozzle  F.  The  ignition  takes 
place  in  the  long  fusiform  chamber  in  which  a  perforated  brick 
tuyere  helps  to  raise  the  temperature  and  act  as  a  re-igniter.  An 
igniting-plug  of  coke  or  carbon  is  pre-heated  and  inserted  by 
the  handle  T  to  start  combustion. 


496 


THE  GAS-ENGINE. 


In  the  burner  principle  of  Sidney  A.  Reeve  of  1897  both  air 
and  fuel  were  supplied  by  separate  pumps,  and  the  proportions 


FIG.  217. 

maintained  by  maintaining  equal  pressures  in  two  receivers 
which  these  pumps  supplied.  A  loaded  check-valve  maintained 
a  pressure  in  the  receivers  higher  than  that  in  the  combustion- 


ENGINES   WITH  HEATING  AT  CONSTANT  PRESSURE.       497 

chamber.  In  the  enlarged  detail  (Fig.  217)  the  pressure  is 
equalized  by  a  diaphragm  4  with  springs  adjusted  on  its  back. 
The  diaphragm  actuates  a  plunger  6  in  a  perforated  sleeve. 
Gas  enters  through  the  central  tube  ior  and  air  through  10  around 
the  central  gas- current.  The  ignition  takes  place  at  b.  The 
water-seal  is  kept  automatically  at  a  desired  level  by  a  float  in 


FIG.  218. 

an  auxiliary  chamber,  and  by  its  presence  the  hot  gases  are  kept 
at  a  constant  pressure  corresponding  to  that  of  saturated  steam 
at  that  temperature,  and  with  a  constant  difference  of  pressure  at 
the  discharge  point  from  that  at  the  supply  point. 

213.  The  Brayton  Engine. — This  engine  (Fig.  218)  had  the 
air  compressed  in  the  pump  B,  whose  volume  was  one-half  that 


THE  GAS-ENGINE. 


of  the  power  cylinder  A.    The  two  constant-pressure  tanks  at 
the  base  of  the  frame  delivered  the  air  through  the  pipe  O  in 


Fig.   219,  which  is  the  burner  for  the  oil-engine,  and  passed  it 
through  the  absorbent  material  or  wick  b  to  which  the  oil  was 


ENGINES   WITH  HEATING  AT  CONSTANT  PRESSURE.        499 

fed  by  a  pump.  The  air  and  fuel  combine  here  so  that  the  air 
becomes  carburated  (par.  107)  and  passes  through  a  wire-gauze 
grating  p  into  the  cylinder  d,  where  it  burns  on  meeting  the  flame 
on  the  bottom  of  the  gauze.  The  air  is  never  completely  shut  off 
by  the  admission- valve  on  its  nominal  closure,  but  enough  always 
flows  through  /  to  keep  a  small  flame  alight.  This  flame  increases 
in  volume  for  the  power  stroke.  Combinations  of  steam  and 
products-of-combustion  engines  belong  in  this  class.  In  Fig.  220 
is  shown  a  steam-boiler  with  a  feed-water  heater  utilizing  waste 
heat  in  the  escaping  gases.  The  air  and  gas  burn  first  in  an 
open  fire-box  to  start  the  engine  with  steam,  and  later,  when  the 
engine  itself  can  compress  the  air  and  gas  mixture,  the  fire-box 
and  chimney  are  closed,  and  the  engine  works  on  a  circuit  of 
gas  and  steam  which  escape  together  from  the  exhaust-pipe  after 
going  through  the  coil. 

214.  Apparatus  for  Observing  Increase  in  Volume  witb 
Constant-pressure  Heating. — The  inconvenient  limits  of  size  for 
an  apparatus  in  which  the  maximum  heating  effect  could  be  ob- 


FlG.  221. 

served  as  producing  a  maximum  increase  of  volume  at  constant 
pressure  resulted  in  the  design  of  the  apparatus  by  Dr.  C.  E. 
Lucke  which  is  shown  in  Fig.  221.  It  depends  for  its  action 
on  the  principles  of  gas  flow  through  an  orifice.  The  rate  of 


500  THE  GAS  ENGINE. 

flow  of  a  gas  though  an  orifice  is  proportional  to  the  form  of 
orifice  and  to  the  pressure  drop  through  the  orifice.  Now  if  the 
gas  be  caused  to  pass  through  a  hole  in  a  plate  before  combus- 
tion, and  later,  after  combustion,  pass  through  a  similar  hole  in 
a  similar  plate,  the  constant  due  to  the  form  of  orifice  would 
be  eliminated  in  comparing  velocities  through  the  two  holes. 
Secondly,  when  the  fall  in  pressure  through  each  hole  is  the  same 
the  velocity  of  flow  through  each  plate  will  be  equal,  and  the 
volume  passing  will  be  proportional  to  the  area  of  the  orifice 
only  if  the  pressures  used  La  small  enough  to  make  correction 
for  compression  vanishingly  small.  Gas  and  air  are  mixed  in 
any  proportion  desired  at  the  compressor  intake  and  delivered, 
mixed,  to  the  chamber  AB,  from  which  the  mixture  will  pass  to 
the  upper  chamber  C  through  a  hole  in  the  plate  secured  between 
the  flanges.  In  chamber  C  there  is  placed  a  cone  of  brick  to 
keep  the  lower  plate  cool,  and  in  the  cone  is  placed  broken  rock 
to  permit  of  the  combustion  of  the  explosive  mixture.  The  top 
plate  between  the  flange  D  is  provided  with  asbestos  sheets  to 
keep  the  hot  gases  from  chilling  just  before  issuing. 

Both  the  brick  cone  for  the  lower  and  the  asbestos  sheet 
protection  for  the  upper  plates  can  be  removed  for  the  taking  of 
observations,  and  a  one-inch  lining  of  fire-clay  can  be  supplied 
to  prevent  radiation.  Mercury  manometers  to  both  chambers 
indicate  the  interior  pressures,  and  hence  the  drop  in  pressure 
through  each  plate. 

215.  The  Future  of  the  Engine  which  uses  Constant-pressure 
Heating  of  the  Working  Medium.  The  Gas-turbine.  —  The 
author  believes  that  in  the  future  there  will  be  increasing  atten- 
tion given  to  the  engine  which  operates  under  the  constant-pressure 
heating  cycle.  The  motor  may  be  either  a  reciprocating  or  a 
continuous  rotary  one,  of  the  turbine  order.  If  a  reciprocating 
engine,  it  will  be  a  compromise  between  the  original  Brayton 
and  the  present  Diesel  types,  avoiding  the  inconveniently  high 
compression  of  the  latter,  and  improving  on  the  mechanical 
design  of  the  former.  Arrong  the  advantages  accruing  from  the 


ENGINES   WITH  HEATING  AT  CONSTANT  PRESSURE         501 

use  of  this  cycle  other  than  the  theoretical  ones  already  referred 
to--in  the  foregoing  may  be  listed : 

(1)  The  avoidance  of  the  sudden  changes  of  pressure  in  the 
cylinder.     The    suddenness    of  these    changes    in   the  constani- 
volume  cycle  is  the  cause  of  the  difficulty  in  obtaining  a  uniform 
turning  effort  in  these  motors. 

(2)  The  work  diagram  becomes  more  flexible,  and  the  control 
of  the  effort  more  perfect  in  its  adjustment  to  the  resistance.     The 
turning  effort  on  the  crank  is  more  nearly  uniform  throughout 
the  cycle. 

(3)  The  motor  becomes  more  easily  reversible,  and  approaches 
the  flexibility  of  the  steam-engine. 

(4)  Low-grade  liquid  fuels  are  easily  used. 

(5)  High  compression  and  its  good  economy  are  easily  secured 
without  danger  of  pre-ignitions. 

With  respect  to  the  development  of  this  cycle  for  application 
in  engines  of  the  turbine  class,  which  are  particularly  adapted 
to  work  under  just  these  conditions,  it  must  be  said  as  yet  that 
the  uncertainties  concerning  the  transformation  of  heat  energy 
into  kinetic  energy  in  a  free  expansion,  and  the  problems  as  to 
suitable  structural  materials  at  high  temperatures,  make  it  pre- 
mature at  present  to  pursue  this  attractive  path  beyond  this 
point.  Success  will  be  likely  to  follow  only  from  considerable 
further  expenditure  of  time  in  research  and  capital  in  experi- 
ment. The  gas- turbine  would  be  specially  valuable  if  it  could  be 
made  to  operate  under  pressures  not  greatly  above  atmosphere, 
while  utilizing  high  initial  temperatures  and  large  increases  of 
volume. 


CHAPTER  XIX. 

TESTS  ON  EXPLOSIVE  MIXTURES. 

220.  Introductory. — The  theoretical  computations  made  in 
connection  with  paragraph  20  have  indicated  the  accepted  method 
of  arriving  at  the  rise  in  temperature  which  follows  from  an 
ignition  of  a  fuel  which  contains  the  necessary  amount  of  oxygen 
to  produce  so  rapid  a  combustion  as  to  be  designated  as  an  ex- 
plosion, which  again  is  the  result  of  the  practically  instantaneous 
propagation  of  a  flame  introduced  into  the  mixture  at  one  point. 
The  condition  of  such  ignition  is  that  present  in  every  explosive 
gas-engine  where  the  mixture  of  gas  and  air  is  ignited  in  the  con- 
stant volume  of  the  combustion- chamber,  which  is  filled  by  the 
explosive  mixture  at  the  pressure  resulting  from  the  previous 
compression  and  which  is  ignited  by  the  electric  spark  or  what- 
ever igniting  device  is  used.  It  becomes  a  matter  of  considerable 
interest  to  compare  the  theoretical  pressures  and  temperatures 
with  those  which  are  actually  realized  in  real  engines  or  under 
the  conditions  which  prevail  with  respect  to  the  presence  of  vary- 
ing volumes  of  fuel  and  air,  or  varying  volumes  of  neutral  or 
incombustible  gases  in  the  explosive  mixture  itself. 

A  diagram  may  be  drawn  presenting  graphically  the  tem- 
perature value  as  computed  theoretically  from  the  formula 

Q 


(par.  55)  for  a  gas  in  which  Q  is  649  B.T.U.  per  cubic  foot, 
whose  weight  is  0.03348  pound  per  cubic  foot,  while  x  is  the 
weight  of  a  cubic  foot  of  air,  or  0.08073.  It  would  give  the  curve 
below  (Fig.  222). 


TESTS  ON  EXPLOSIVE  MIXTURES. 


505 


It  will  be  apparent  that  the  better  the  explosion  process  in  any 
engine,  the  smaller  the  cylinder  volume  which  will  be  required 
to  overcome  a  given  mechanical  resistance.  Hence  an  explosive 
mixture  will  be  called  the  best  which  produces  the  greatest  initial 
pressure  for  a  unit  volume;  and  secondly,  that  which  maintains 


TOGO0 


§000° 


4000° 


3000d 


8000° 


aootf 


FlG.  222. 

the  highest  pressure  for  the  longest  time  when  exposed  to  the 
cooling  action  of  the  cylinder  walls  and  jackets.  It  is  a  matter 
of  common  observation  in  gas-engines  that  if  the  piston  be  blocked 
so  that  it  cannot  move,  and  the  compressed  charge  behind  it 
be  ignited,  the  pressure  due  to  the  ignition  will  fall  very  rapidly 
by  reason  of  the  absorption  of  heat  from  the  conducting  walls. 
It  becomes  significant,  therefore,  to  investigate  the  behavior  of 
such  explosive  mixtures. 


5°4 


THE  GAS-ENGINE. 


221.  Clerk's  Explosion  Experiments. — Ttue  standard  English 
experiments  upon  this  question  are  those  of  Mr.  Dugald  Clerk. 
His  apparatus  is  presented  in  Fig.  225,  and  consisted  of  a  closed 


FIG.  225. 

cylindrical  vessel  seven  inches  in  diameter  and  eight  and  one- 
quarter  inches  on  the  inside  "and  holding,  therefore,  317  cubic 
inches.  Upon  one  cover  was  attached  a  steam-engine  indicator 
whose  drum  was  made  to  revolve  by  a  weight  through  multi- 
plying gearing  with  a  fan  governor  to  maintain  a  uniform  speed. 
The  cylinder  was  filled  with  the  mixture  to  be  tested,  the  revolving 
drum  set  in  motion  with  the  pencil-point  bearing  against  it,  and 
an  electric  spark  was  passed  between  terminals  at  the  bottom  of 
the  vessel.  The  rate  of  the  revolution  of  the  indicator- drum  being 
known,  the  interval  of  time  elapsing  between  any  two  points  of  the 
explosion  curve  or  the  cooling  curve  are  at  once  given,  and  the 
position  of  the  highest  pressure  gives  both  the  value  of  that  maxi- 
mum and  the  time  taken  to  reach  it.  The  diagrams  from  such 
an  apparatus  appear  as  in  Fig.  226,  when  mixtures  of  ordinary 
illuminating-gas  and  air  were  tested.  The  following  table  gives 
the  results  of  this  investigation.  It  is  unfortunate  for  the  value 
of  these  results  for  subsequent  comparison  with  other  tests,  that 


TESTS  ON  EXPLOSIVE  MIXTURES. 


505 


their  author  did  not  give  in  some  fulness  the  composition  of  the 
gas  which  he  used.  The  presence  of  more  or  less  percentages 
of  neutrals  or  diluents  in  their  analysis  makes  the  mixtures  behave 


0     .05     .10     .15     .20     .25     .30     .35     .40     .45     .50     .55     .60     .65     .70     .75     .80     .85    .90     .95   1JOO 


FIG.  226. 


quite  differently  at  different  times.  Mr.  Clerk  simply  calls  the 
gas  Glasgow  and  Oldham  gas,  and  published  analyses  taken  at 
some  other  time  cannot  always  be  connected  safely  to  these  data. 


I 

2 

3 

4 

5 

6 

7 

Proportions. 

Maximum 
Observed 
Pressure, 
Lbs.  per 
Sq.  In. 

Time  to 
Reach 
Maximum 
Pressure, 
Seconds. 

Pressure 
Celculated 
Due  to 
i  Cu.  In. 
Gas. 

Pressure 

after 
0.2  Second 
after 
Maximum. 

Col.  s+Col.  6 

Gas. 

Air. 

2 

14 
13 
12 
II 
10 

9 
8 

6 

5 
4 

40 

f-5 
60 

61 

0-45 
0.31 
0.24 
0.17 

728 

602 

665 

756 

576 

666 

690 

47° 

580 

78 

O.o8 

712 

440 

556 

87 
90 

Qi 

80 

O.o6 
0.04 

°-°5S 
0.16 

576 

342 

459 

Temperature  before  explosion  60°  F.     Pressure  atmospheric. 


5o6 


THE  GAS-ENGINE. 


With  a  mixture  of  hydrogen  and  air  instead  of  gas  and  air 
at  55°  F.  the  following  results  showed  that  it  was  inferior  to  coal- 
gas,  as  follows: 


I 

2 

.3 

4 

Proportions. 

Maximum 
Observed 

Time  to  Reach 

Pressure, 

Maximum  Pressure, 

Pounds  per 

Seconds. 

Hydrogen. 

Air. 

Square  Inch. 

I 

6 

41 

0.15 

I 

4 

68 

0.026 

2 

5 

80 

O.OI 

This  investigation  as  presented  in  the  curves  seems  to  indicate 
that  the  best  results  with  respect  to  pressure  are  given  with  one 
volume  of  gas  to  five  volumes  of  air,  and  that  as  the  dilution  with 
air  increases,  the  area  of  work  under  the  curve  would  diminish. 
The  rapidity  of  the  ignition  in  these  proportions  makes  an  in- 
convenient shock  in  the  cylinder.  If,  now,  the  pressures  in  the 
third  column  resulting  from  explosion  are  reduced  in  common 
ratio  so  as  to  give  the  volume  which  they  occupy  with  equal 
pressures  from  a  uniform  volume  of  gas  ignited,  such  as  one  cubic 
inch,  the  fifth  column  of  the  table  results. 

If  now  from  the  diagram  of  pressures  the  pressure  existing 
after  one-fifth  of  a  second  be  scaled  off,  a  measure  is  found  for 
the  cooling  effect  «of  the  walls  in  an  engine  making  300  revolutions 
per  minute.  This  pressure  tabulated  in  the  6th  column  can  be 
used  to  compute  the  yth  column,  which  should  give  the  highest 
arithmetical  mean  of  the  explosion  effect  and  cooling  effect  with 
five  strokes  to  the  second.  This  column  indicates  that  the  best 
results  with  respect  to  mean  pressure  are  given  when  the  ratio 
of  gas  to  air  is  between  one-twelfth  and  one-fourteenth.  Both 
with  less  gas  and  with  more  the  mean  pressure  falls  off.  Clerk's 
experiments  with  hydrogen,  reported  in  the  second  table,  showed 
that  it  was  not  equal  to  the  ordinary  illuminating-gas  volume 
for  volume.  Two  volumes  of  hydrogen  to  five  volumes  of  air 
gave  a  pressure  of  80  pounds  in  one  one-hundredth  of  a  second, 


TESTS  ON  EXPLOSIVE  MIXTURES. 


507 


while  with  illuminating-gas  the  same  pressure  resulted  from  a 
mixture  of  one  of  gas  to  ten  of  air,  with  a  combustion  which  was 
not  so  inconveniently  rapid  as  to  cause  undue  shock,  jar,  or 
vibration  in  the  motor. 

222.  Lucke's  Explosion  Experiments. — The  apparatus  used 
by  Dr.  Charles  E.  Lucke  in  determining  the  pressures  caused 
by  explosion  or  by  combustion  at  constant  volume  is  shown  in 
Fig.  227.  To  a  tee  A  were  attached  two  nipples  B  closed  with 


FIG.  227. 

caps  C  above  and. below.  To  the  branch  of  the  tee  was  con- 
nected an  indicator,  and  the  igniting  arrangement  was  attached 
in  one  branch  of  a  three-way  cock  on  the  upper  cap.  The  appara- 
tus was  first  filled  with  water  through  the  connection  controlled 
by  the  valve  F  at  the  bottom  until  the  water  overflowed  through 


508  THE   GAS  ENGINE. 

the  valve  G,  with  the  three-way  cock  in  position  to  isolate  the 
spark-plug  but  fill  the  apparatus  completely  and  expel  the  air.. 
When  completely  filled  the  water- valves  G  and  F  are  closed  and 
H  and  /  open.  The  mixture  to  be  tested  in  a  closed  tank  under 
pressure  flows  through  H  and  the  opened  three-way  cock,  and 
the  water  is  expelled.  When  the  three-way  cock  is  reversed  end 
the  outlet  /  closed  the  mixture  in  the  explosion  vessel  is  at  atmos- 
pheric pressure  and  can  be  fired  by  the  spark- points,  while  the 
pressure  on  the  indicator  draws  a  diagram  giving  pressure  and 
time  values  as  in  the  Clerk  apparatus. 

While  this  investigation  covered  research  into  the  heat  de- 
veloped by  combustion  at  constant  pressure,  yet  for  the  present 
purpose  attention  is  mainly  directed  to  the  effect  on  the  pressures 
at  constant- volume  combustion,  as  these  are  affected  by  varying 
constitution  of  the  mixture  from  the  presence  of  neutral  gases, 
which  are  inert  so  far  as  producing  temperature  and  pressure 
are  concerned.  If  the  gas  be  assumed,  for  example,  to  have  a 
standard  composition,  such  as: 

C02 3-8 

c2H4 : i4.6 

CO 28 .  o 

H 35-6 

CH4 16.7 

N 1.3 


Total 100. o 

of  this  there  will  be 

NEUTRAL. 

C02 3.8 

N i- 


Total 5.1 

Such  a  gas,  moreover,  will  yield  691.59  B.T.U.  per  cubic  foot 
products  condensed,  and  in  its  combustion  wTill  call  for  5.21  parts 
of  air  per  one  part  of  gas. 


TESTS   ON  EXPLOSIVE  MIXTURES. 


509 


A  chemical  mixture  then  would  have  these  characteristics: 

Air 5-21  volumes 

Gas.  .  .   i. oo 


Total. 


of  which 


,  (  Neutral  in  gas.. 
Neutral  j  Nitrogen  in  air. . 


6.21 

-051 

4.120 


Total  neutral. .  4.17 
in  6.21  parts,  or  67  per  cent  neutral. 

Various  mixtures  of  this  gas  and  air  will  give 


PflQ 

Air  

3  -° 

3.5 

4.0 

4.5 

5.0 

5-5 

6.0 

6.5 

7-0 

.  29 

•  79 

i  .  29 

i  .  79 

Active  air  

3  «° 

3.5 

4.0 

4.5 

5.0 

5.  21 

5-  21 

5-  21 

5  .  21 

Inactive  gas,  i.e.,  excess  
Active  gas  

.427 
•  573 

.328 
.672 

.232 
.768 

.135 
.865 

.050 
•  95° 

I  .000 

i  .000 

I  .000 

I  .000 

Neutral  in  active  air  
Neutral  in  active  gas  

2.372 
.029 

2.768 
.034 

3-163 
.039 

3-559 
.044 

3-954 
.048 

4.  I2O 

.051 

4.  1  20 

.051 

4.  I2O 

.051 

4.  120 

.051 

Total  inactive  or  excess.  .  . 

2.828 

3  •  i  3O 

3  •  434 

3  .  735 

4.052 

4.  461 

4.  961 

5.461 

5  -961 

701 

.696 

.687 

.680 

.675 

.686 

.  704 

•  729 

.746 

It  should  be  noted  how  very  slightly  the  increase  in  percentage 
of  dilution  increases  with  the  excesses  of  air  and  gas;  though  the 
proportions  may  vary  over  100  per  cent,  the  dilution  varies  through 
but  little  more  than  5  per  cent.  There  can  be  little  doubt  that 
the  limits  of  combustibility  are  intimately  associated  with  the 
per  cent  of  neutral  or  inactive  gases  present. 

On  examination  of  the  calorific  values  of  some  of  these  mix- 
tures, i.e.,  the  amount  of  heat  which  one  cubic  foot  of  gas  can 
deliver  when  burned  explosively  in  mixtures  within  the  limits  of 
explosive  combustion,  it  will  appear  that  the  heat  developed  by 
a  cubic  foot  of  the  gas  in  question  is  691.59  B.T.U.  when  com- 
pletely burned,  i.e.,  in  a  chemical  mixture,  or  in  a  mixture  in 
which  air  is  in  excess,  within  of  course  the  limits  of  combusti- 
bility. Hence, 


Gas  .  .. 

Air  
Gas  burnt,  i.e.,  gas  that  could  find 
air  enough  to  burn  it  
B.T.U.  available  

3-0 

•  573 
396.3 

3-5 

.672 
464-8 

4.0 

.768 
531-2 

4-5 

.865 
598.2 

S.o 

-950 
657-0 

5-5 

T  .000 

691  .6 

6.0 

I  .000 

691  .6 

6.5 

I  .000 

691  .6 

7.0 

i  .000 
691.6 

510 


THE   GAS-ENGINE. 


These  results  are  shown  graphically  on  the  curve  A  of  Fig 
228.     The  results  are  as  follows,  reduced  to  cubic  feet  of  gas: 

B.T.U.  PER  CUBIC  FOOT  OF  GAS  WHEN  MIXED  WITH  AIR. 

Gas.  Air.  B.T  U.  per  cu.  ft.  Gas. 

3.0  275.1 

3-5  347-82 

4-0  401-57 

4.5  471.00 

5.0  541-7° 

5-5  616.59 

6.0  600.78 
6-5  ? 

Each  mixture  of  air  to  gas  within  the  range  of  combustibility 
was  fired,  and  then  to  each  was  added  in  turn  successively  in- 


700 


Q 

x  500 

i 


.  400 


;3oo 


\ 


JJ  300 


100 


345 

PARTS  AIR  PER  ONE  PART  GAS. 
FIG.  228. 


creasing  amounts  of  neutral    gases  obtained  by  burning  com- 
pletely an  explosive  mixture. 

It  appeared  that  the  resulting  pressures  were  intimately  con- 
nected with  the  percentage  of  dilution  of  neutral  or  excess  gases, 


TESTS   ON  EXPLOSIVE  MIXTURES. 


and  as  the  gas  used  has  already  exhibited  some  agreement  with 
what  is  possible  with  the  typical  water-gas  chosen  in  comparison, 
it  will'  be  well  to  work  out  a  table  of  percentage  of  dilution  of  differ- 
ent mixtures,  and  these  figures  will  be  placed  on  the  curves  of 
Figs.  229-234.  The  agreement  and  evident  existence  of  a  law 
is  apparent. 

WATER-GAS  or  OBSERVED  COMPOSITION. 

Mixture,  \  ^  3  I  diluted. 
I  Gas,  i  \ 


Gas. 

Air. 

Added 
Neutral. 

Primary 
-Neutral. 

Total 
Neutral. 

Per  Cent 

Neutral. 

I 

3. 

O 

2-83 

2.83 

70.1 

I 

3 

I 

it 

3-83 

76.0 

I 

3 

2 

<t 

4-83 

80.5 

I 

3 

3 

(.( 

5-83 

83.0 

Mixture, 


diluted. 


Gas. 

Air. 

Added 
Neutral. 

Primary 
Neutral. 

Total 
Neutral. 

Per  Cent 
Neutral. 

I 

4 

0 

3-43 

3-43 

68.7 

I 

4 

I 

" 

4-43 

74-o 

I 

4 

2 

" 

5-43 

77-6 

I 

4 

3 

" 

6-43 

80.6 

I 

4 

4 

7-43 

82.8 

Mixture, 


I  Air,   5 
1  Gas,  i 


diluted. 


Gas. 

Air. 

Added 
Neutral. 

Primary 
Neutral. 

Total 

Neutral. 

Per  Cent 
Neutral. 

5 

0 

4-05 

4-05 

67-5 

S 

I 

5-05 

72.1 

5 

2 

H 

6.05 

75-7 

5 

3 

a 

7-05 

78-4 

5 

4 

« 

8-05 

80.5 

THE   GAS-ENGINE. 


Mixture,  •!     ™'      }•  diluted. 
(Gas,  i) 


Gas. 

Air. 

Added 
Neutral. 

Primary 
Neutral. 

Total 
Neutral. 

Per  Cent. 
Neutral. 

I 

6 

O 

4.96 

4.96 

70.4 

I 

6 

I 

" 

5-96 

74-4 

I 

6 

2 

a 

6.96 

77-3 

I 

6 

3 

(C 

7.96 

79-6 

I 

6 

4 

a 

8.96 

81.3 

I 

6 

5 

9.96 

84.0 

Mixture, 


(Air,   7 
1  Gas,  i 


diluted. 


Gas. 

Air. 

Added 
Neutral. 

Primary 
Neutral. 

Total 

Neutral. 

Per  Cent 
Neutral. 

I 

7 

0 

5-96 

5-96 

74-6 

I 

7 

I 

6.96 

77-3 

I 

7 

2 

a 

7.96 

79.6 

T 

7 

3 

PC 

8.96 

81.3 

I 

7 

4 

9^96 

83.0 

The  curves  of  Figs.  229-233  show  the  pressures  given  by  the 
indicator  for  each  mixture  and  are  the  mean  values  from  a  large 
number  of  lines  drawn  by  the  indicator.  These  curves  are  com- 
bined in  Fig.  234,  which  is,  therefore,  a  curve  of  pressures  for  all 
mixtures  diluted  or  not  within  the  range  of  explosive  combusti- 
bility. The  numbers  on  the  curves  show  the  percentage  of 
dilution  of  the  typical  water-gas.  The  results  are  most  remark- 
able and  can  be  accounted  for  only  by  assuming  that  the  presence 
of  a  large  amount  of  dilution  hinders  combustion.  The  limits 
at  which  combustion  ceases  to  be  possible  on  too  great  a  dilution 
are  here  indicated,  whether  that  dilution  be  due  to  excess  gas, 
excess  air,  or  neutral  gases.  It  will  also  be  observed  that  the 
character  of  the  diluent  has  an  appreciable  effect,  but  that  when 
the  dilution  is  least  the  pressure  is  greatest,  about  60  pounds 
above  atmosphere  or  a  ratio  of  5 ;  and  the  presence  of  a  constant 
per  cent  of  neutral  will  make  combustion  impossible  no  matter 


TESTS   ON  EXPLOSIVE  MIXTURES. 


513 


80 


15 


1  2  3 

PARTS  NEUTRAL  ADDED 


FIG.  230. 


FIG.  231. 


I  45 

CO 


30 


3       4  1 

PARTS  NEUTRAL  ADDED, 


FIG.  232. 


FIG.  233. 


4  4.5  5  5.5 

PARTS  AIR  PER  ONE  PART  GAS. 


0.5 


FIG.  234. 


514  THE  GAS-ENGINE. 

what  the  mixture  of  air  and  gar,.  The  greatest  neutral  dilution 
gives  the  least  pressure — about  15  pounds  above  atmosphere, 
or  a  ratio  of  about  2.  These  results  give  a  reason  for  the  de- 
creased pressure  in  exploding  gas-engines  in  which  the  mixture 
is  always  diluted  by  burnt  products  to  an  extent  of  20-40  per  cent 
of  the  volume  of  neutral  addition  to  the  gas  mixture,  which  may 
already  have  neutral  gas  present  to  the  extent  of  65-70  per  cent. 

.  Neutral  additions  to  the  gases  sent  to  the  calorimeter  and  to 
the  other  apparatus  showed,  besides  a  corresponding  and  proper 
heat  value  for  the  resulting  mixture,  a  decreased  rate  of  propaga- 
tion accompanied  by  a  difficulty  in  ignition  and  constant  ten- 
dency to  incomplete  combustion,  i.e.,  tendency  to  cease  burning 
after  inflammation  had  been  started  and  before  the  mass  had 
been  entirely  burnt. 

223.  The  Massachusetts  Institute  of  Technology  Experiments 
on  Explosive  Mixtures. — In  1898  an  experimental  apparatus 
was  fitted  up  in  the  laboratories  of  the  above  Institute  in  Boston, 
and  results  from  it  have  been  published  from  time  to  time.  The 
apparatus  is  a  cast-iron  cylinder  with  a  flanged  top  to  which  is 
bolted  the  cover.  The  mixture  is  introduced  and  proportioned 
by  the  plan  of  exhausting  the  test-chamber  by  a  pump  to  remove 
all  previous  charge,  and  is  then  scavenged  by  admitting  fresh 
clean  air.  It  is  then  exhausted  again  by  the  pump  until  a  desired 
pressure  lower  than  atmosphere  is  reached,  so  computed  that 
when  gas  at  atmospheric  pressure  is  introduced  the  rise  of  pressure 
in  the  chamber  to  atmospheric  pressure  shall  draw  in  just  the 
desired  volume  of  gas.  Pressures  above  atmosphere  can  be 
used  if  desired  by  having  suitable  pumps  and  computed  vol- 
umes adjusted  to  the  higher  pressures.  This  method  of  pro- 
portioning is  not  believed  to  be  as  reliable  as  that  followed  in 
the  preceding  paragraph,  in  view  of  the  fact  that  the  volumes 
are  not  directly  measured. 

The  indicator  makes  its  record  upon  a  card  on  a  power- 
driven  disk,  upon  which  the  time  record  is  simultaneously  made 
by  the  vibrations  of  a  tuning-fork,  kept  moving  by  an  electro- 


TESTS   ON  EXPLOSIVE  MIXTURES.  515 

magnet.  A  pointer  on  one  arm  of  the  fork  traces  the  time  line. 
The  mixtures  are  fired  electrically.  The  same  fifth- of- a- second 
limit  was-  used  as  chosen  by  Clerk,  in  correspondence  with  an 
engine  running  at  300  r.p.m.  The  analysis  of  the  gas  was: 

CO 25.3 

Illuminants 12.0 

C09. 


CH4. 

N. .. 
H. .. 
O.  . 


IOO.O 


RESULTS  OF  TESTS  ON  EXPLOSIVE  MIXTURES  OF  ILLUMINATING- 
GAS  AND  AIR. 


2 

First  %  Second. 

^  Second  after  Maximum  Pressure. 

Mixture.  (By  Par 

Maximum  Pressure 
(Lbs.  per  Sq.  In. 

Time  of  Explosion. 
(Seconds.) 

£ 

OJ 

1 

3 

Mean  Pressure 
(Lbs.  per  Sq.  In.) 

Mean  Pressure  -e- 
Proportion  of  Gas. 

Final  Pressure. 

Area.  (Square 
Inches  ) 

UhJ 

Mean  Pressure  -i- 
Proportion  of  Gas. 

Final  Pressure. 

Final  Pressure  -4- 
Proportjon  of  Gas. 

i 

2 

3 

4 

5 

6 

7 

8 

9 

TO 

i< 

12 

Gas-  Air. 

1-3 

45 

-49 

0.32 

II 

44 

26 

-jo 

43 

172 

40 

1  60 

1-4 

86 

.08 

-77 

59 

295 

61 

.88 

62 

310 

46    230 

*~5 

96 

-°5 

.86 

62 

372 

S2 

-93 

64 

384 

44 

264 

i-6 

88 

-°5 

.80 

60 

420 

54 

-93 

64 

448 

46 

322 

1-7 

86 

.06 

-97 

66 

528 

58 

-93 

64 

512 

48 

384 

!-8 

87 

.06 

-71 

57 

5*3 

53 

-83 

61 

549 

46 

414 

1-9 

77 

.08 

.60 

53 

53° 

57 

.86 

62 

620 

46 

460 

I-IO 

71 

.11 

-36 

45 

495 

56 

1.69 

56 

616 

45 

495 

I-II 

68 

.14 

.21 

40 

480 

60 

1.66 

55 

660 

43 

I-I2 

39 

-33 

o-35 

12 

156 

29 

0.98 

33 

429 

30 

39° 

I-I3 

32 

.42 

0.18 

6 

84 

16 

o-79 

26 

364 

24 

336 

I-I4 

9 

.42 

0.05 

2 

3° 

4 

0.24 

8 

120 

8 

I2O 

The  diagrams  developed  on  a  straight  base-line  give  the  results 
in  Fig.  235. 


THE  GAS-ENGINE. 


From  these  it  appears  that  while  the  15.4  percentage  of  gas 
gives  the  greatest  initial  pressure,  the  rate  of  cooling  is  also  greater, 
so  that,  as  in  the  other  experiments,  a  mixture  with  9  to  10  per  cent 


10 


45 


50 


55 


30  25  30  35  40 

TLME  IN  SIXTIETHS  OF  A  SECOND. 
FIG.  23?. 


of  gas  gives  the  greatest  average  pressure  for  the  first  fifth  of  a 
second. 

Fig.  236  shows  the  effect  of  varying  the  composition  of  the 
mixture  both  as  to  the  time  taken  to  reach  the  maximum  pressure 
and  the  value  of  that  maximum. 

The  quickest  explosion,  as  elsewhere  noted,  gives  the  maxi- 
mum pressure.  The  two  following  tables  give  interesting  data 
from  the  same  source  concerning  mixtures  of  air  and  gasoline. 


TESTS  ON  EXPLOSIVE  MIXTURES 
GASOLINE  (86°,  Sp.  gr.  0.648)  AND  AIR. 


i 

1 

First  0.2  Second. 

0.2  Sec.  after  Maximum  Pressure. 

M 

Oj 
O 

d 

OJO 

•!•  M 

fj 

<u°O 

.1.  <"' 

v 

,-N 

VH    C 

12 

3 
I 

X-x 

v«  C 

go 

£ 

fi 

X 
W 

d 

hH 
1 

i 

03    O 

j 

1 

d 

IT 

n 

w  cr 

(H    '*-' 

03    O 

:ssure. 

1  ' 

IS 

^ 

c  R 

£ 

0 

«§ 

c  ? 

& 

1 

I 

d 

§^ 

oj  o 

d 

I 

oj 

6 

£3 

d  o 

"~a 

A 

P 

1 

£~ 

S^ 

£ 

S 

S~ 

§^ 

£ 

.0151 

-083 

1.40 

46.7 

3080 

46 

70 

.48 

49-4 

3260 

34 

.0164 

.100 

I.4I 

47-o 

2865 

49 

73 

-53 

51.0 

3110 

36 

.0179 

.090 

1.33 

44-3 

2480 

44 

71 

-43 

47-7 

2670 

33 

.0196 

.083 

1.36 

45-3 

2309 

46 

76 

-55 

2634 

35 

.0217 

.058 

i-34 

44-7 

2055 

37 

70 

-45 

48.4 

2225 

3° 

.0244 

.067 

1.50 

50.0 

2050 

44 

80 

.60 

53-4 

2190 

36 

.0256 

-075 

i.  60 

53-4 

2081 

5° 

84 

.69 

56-4 

220O 

40 

.0263 

-059 

1.65 

2089 

46 

86 

-71 

57-o 

2164 

38 

.0278 

-083 

1.41 

47-o 

1691 

48 

78 

.62 

54-o 

I945 

36 

-0303 

.091 

1.40 

46.7 

1541 

52 

76 

.60 

53-4 

1760 

38 

-0323 

.083 

i-45 

48.4 

1500 

48 

77 

.62 

54-o 

l675 

37 

-0345 

.083 

1.51 

5°-3 

1467 

48 

77 

-64 

54-7 

1587 

37 

-0385 

-075 

1.37 

45-7 

1188 

47 

66 

.^o 

50.0 

1300 

38 

.0417 

.066 

1.25 

42-7 

1025 

41 

60 

-38 

46.0 

1104 

35 

.0476 

.066 

1-15 

38-4 

608 

39 

56 

-32 

44-o 

925 

33 

GASOLINE  (76°,  Sp.  gr.  0.680)  AND  AIR. 


a 

8 

CO 

First  0.2  Second. 

0.2  Sec.  after  Maximum  Pressure. 

i 

d 

oJ'-T1 

*  a 

§ 

• 

«7 

•1-  IS 

*o5 

M 

o 
1 

A 

d 

?M 

p 

g 

i 

d 
i—  i 

VH    C 

P 

go 

| 

M 

U* 

u) 

w  n 

t/3 

61 

«    u. 

IH    ^ 

• 

JS 

H 

8 

£  p, 

1 

I 

i 

CO 

£l 

1 

1 

"£ 

*o 

• 

& 

g 

o 

PH 

0 

1 

H 

ci 

1 

JS 

rt  g 

£ 

1 

1 

|§ 

j| 

£ 

.0132 

.167 

.76 

25-3 

1925 

52 

52 

.28 

42-7 

3240 

33 

.0141  ' 

.117 

•  r5 

38.4 

2720 

49 

62 

.42 

47-3 

336° 

35 

.0151 

.109 

.26 

42.0 

2770 

48 

64 

-45 

48.6 

295° 

35 

.0164 

.182 

.81 

27.0 

1650 

50 

51 

-25 

41.7 

2540 

.0179 

.109 

-27 

42.3 

2368 

5° 

67 

-53 

51.0 

2855 

36 

.0196 

.091 

-44 

48.0 

2441 

48 

73 

-53 

51.0 

2600 

36 

.0217 

.082 

-43 

47-7 

2l8o 

48 

76 

-56 

52.0 

2391 

37 

.0244 

.060 

.62 

54-o 

2213 

45 

85 

-63 

54-3 

2225 

36 

.0263 

.0^8 

.61 

53-7 

2040 

45 

85 

.62 

54-o 

2052 

36 

.0278 

.o=;8 

.62 

54-o 

J943 

46 

84 

.64 

54-7 

1970 

38 

-0303 

.066 

-49 

49-7 

1640 

45 

78 

.60 

53-4 

1760 

-0323 

.067 

-55 

51.7 

1602 

48 

83 

.70 

56.7 

1760 

38 

-0345 

.100 

-34 

44-7 

1297 

52 

75 

-59 

53-o 

J536 

38 

-0385 

.117 

.10 

36.7 

955  1  52 

62 

.42 

47-3 

1230 

35 

.0417 

-133 

.98 

32-7 

761 

52 

55 

1.40 

46.7 

II2I 

38 

.0476 

.210 

-39 

13.0 

273 

35 

35 

i.  02 

34-o 

7M 

32 

THE  GAS-ENGINE. 


The  greatest  value  for  the  mean  pressure  during  the  explo- 
sion period  is  found  for  both  cases  in  the  neighborheod  of  25 
parts  in  1000,  or  2^  per  cent  of  gas  in  one  hundred  of  the  mixture. 


10  12  14  16  .18  20  22 

PER  CENT  GAS  IN  MIXTURE. 

FIG.  236. 

224.  Grover's  Experiments  with   Acetylene. — A   third  group 
of  explosion  experiments  include  those  of  Mr.  Frederick  Grover  of 


TESTS  ON  EXPLOSIVE,  MIXTURES. 


5*9 


Leeds,  England,  between  1899  and  1901.  The  explosion-chamber 
was  a  piece  of  cast-iron  flanged  pipe.  An  indicator  outfit  gave 
the  pressures  due  to  the  ignition,  effected  by  electric  spark.  The 
timing  for  the  speed  of  the  diagram  under  the  indicator  pencil 
was  done  in  a  simple  and  elegant  manner,  by  mounting  a  stop- 
watch ticking  fractions  of  seconds  upon  a  gear  which  was  driven 
through  a  worm  on  the  axis  of  the  paper  drum.  By  revolving 
the  watch  under  the  second  hand  and  in  the  opposite  direction, 
it  is  plain  that  at  the  speed  of  the  second  hand  the  hand  would 
remain  stationary  in  space.  A  mirror  on  the  axis  of  the  hand 
would  show  by  steady  reflection  of  a  fixed  object  when  the  needle 
stood  still  in  space,  and  the  speed  of  the  paper  on  the  drum  was 
easily  computed  when  the  reduction  of  the  gear  driving  the  watch- 
case  was  known.  The  paper  would  always  be  moving  at  the 
same  rate  for  all  experiments. 

The  tests  gave  results  both  of  pressures  on  ignition  and  with 


Maximum  Pressures  JIbs.D 

§  6  §  8  8 

1  L 

^ 

^^ 

*\ 

^ 

^^^b 

^ 

^ 

^*^ 

"^^c 

"^> 

^^ 

r 

c 

-->.. 

-?°«A 

^ 

s^>^ 

_JS 

£^ 

^4. 

^ 

>^> 

8         9        10       11       12       13       14 
Ratio  of  Air  to  Gas  by  Volume. 

FIG.  237. 


15       16       17       18 


various  degrees  of  previous  compression  and  the  time  results 
with  various  mixtures  of  acetylene  and  air.  Compressions  of  one, 
two,  and  three  atmospheres  were  tried,  and  Figs.  237,  238,  and 
239  show  the  pressures  with  acetylene  compared  with  the  same 
mixtures  of  ordinary  coal-gas  and  air.  In  Figs.  240,  241,  and  242 


520 


THE  GAS-ENGINE. 


are  the  pressures  and  the  times  required  to  reach  them.     Acety- 
lene   gives  higher  pressures    than  coal-gas,  although  less  high 


9          10         ll         12          13          14          15          16         17         18          19          20          21 
Ratio  of  Air  to  Gas  by  Volume 


FIG.  238. 


.   ll  ia  is  u  is  16  ar  is  19  go  21  22  23  24  25  20  27 

-X  Batio  oiAir  to  Gas  by  Volume 

FIG.  239. 


01        2        3        4        5        6        7        8        9       10      11      12      13      11      15      .16      17 
Time  in  Hundredths  of  One  Second. 

FIG.  240. 

in  proportion  as  the  compressions  increase.     Coal-gas  requires 
5.7  volumes  of  air  for  its  combustion,  while  acetylene  requires 


TESTS  ON  EXPLOSIVE  MIXTURES.  521 

12.5  volumes.  Acetylene  fires  more  quickly,  as  the  times  ranged 
from  o.i  to  0.018  of  a  second  for  the  proportions  which  reached 
their  maximum  with  coal-gas  in  0.5  and  0.25  of  a  second  re- 


5       6        7        8        9       10      11      12      13      14      15      16      IT     18 
Time  in  Hundredths  of  One  Second 

FIG.  241. 


6        7        8        9       10      11       12      13      It      15      16      17      18 
Time  in-Hundredths  of  a  Second, 


FIG.  242. 

spectively.  The  weakest  proportion  of  acetylene  to  air  which 
would  ignite  is  i  to  18,  while  with  coal-gas  the  limit  is  i  to  15. 
An  analysis  of  the  products  of  combustion  wlien  the  previous 
compression  was  three  atmospheres  gave  the  following  table: 


Mixture. 

Constituent  in  Percentage. 

Air. 

Acetylene. 

C02. 

CO. 

o. 

N. 

Steam. 

II.7 

13.0 

3-2 

0.0 

79-o 

6-5 

12.3 

!5-i 

o.o 

0.0 

78.0 

8.2 

14-5 

12.4 

0.0 

2-5 

78.9 

6.2 

16.1 

n.  8 

0.0 

4.2 

79-o 

5-9     • 

J7-5 

IO.O 

0.0 

5-i 

79-6 

5-° 

21 

8.6 

0.0 

8.1 

78.9 

4-3 

22 

9.0 

0.0 

8.6 

79-o 

4-5 

30 

. 

6.8 

0.0 

12.0 

78.5 

3-4 

522  THE   GAS-ENGINE. 

225.  Grover's  Experiments  on  Effect  of  Neutrals  in  Explosive 
Mixtures. — A  series  of  experiments  in  the  laboratories  of  the 
Yorkshire  College  at  Leeds,  England,  instigated  by  Mr.  G rover 
has  added  much  to  the  knowledge  concerning  the  effect  of  products 
of  combustion  in  the  explosive  charge.  The  apparatus  was 
essentially  the  same  as  in  the  previously  described  research. 
The  charge  consisted  of: 

1.  The  volume  of  neutral  products  of  combustion  from  a 
previous   ignition  which  was   desired  in  proportion  to  the  total 
volume. 

2.  Half  the  volume  of  pure  air  required  to  make  the  com- 
bustible mixture. 

3.  The   full   volume   of   coal-gas   to   make   the   combustible 
mixture. 

4.  The  rest  of  the  volume  of  pure  air  to  complete  the  new 
charge. 

Without  waiting  for  diffusion  the  charge  was  then  fired  at 
atmospheric  pressure. 

The  annexed  diagram  presents  the  results  of  this  research  in 
graphic  form  (Fig.  243).  The  experiments  themselves  and  the 
diagram  may  be  interpreted  as  suggesting: 

1.  The  presence  of  products  of  combustion  does  not  diminish 
the  actual  pressures  as  much  as  that  same  excess  of  air  would 
do,  filling  the  same  volume  of  the  clearance  in  the  cylinder.     This 
is  not  inconsistent  with  the  observed  fact  that  a  scavenging  action 
with  pure  air  has  diminished  gas  consumption,  since  the  effect 
of  that  scavenging  in  cooling  the  cylinder  is  to  increase  the  weight 
of  explosive  mixture  which  fills  a  given   volume  at  that  lower 
temperature,   both  by  removing  the  heating  effect   of  the  hot 
gases,  and  by  making  the  jacket  effect  prove  pronounced. 

2.  The  highest  pressures  are  obtained  when  the  volume  of 
air  in  the  charge  is  only  slightly  in  excess  of  that  required  for 
complete  combustion. 

3.  The  time  of  explosion  is  reduced  when  the  hot  products 
of  combustion  take  the  place  of  cool  fresh  air. 


TESTS   ON  EXPLOSIVE  MIXTURES. 


523 


4.  The  mixture  will  ignite  in  all  cases  where  the  volume  of 
air  exceeds  the  minimum  of  5.5  times  that  of  the  gas  as  required 
for  complete  combustion,  provided  the  proportion  of  neutrals 
present  does  not  exceed  58  per  cent  of  the  combined  mixture  of 


Coal  Gas  Volumes,  per  cent. 

FIG.  243. 

combustible,  necessary  air  for  combustion,  and  the  neutral  products 
taken  together. 

226.  Temperature  of  Ignition  or  Inflammation. — The  re- 
searches of  Sir  Humphry  Davy  showed  that  for  ignition  of  gaseous 
explosive  mixtures  it  was  necessary  that  they  be  brought  to  a 
certain  temperature  at  one  point  before  they  would  ignite.  The 
best  modern  work  along  this  line  has  been  done  by  Berthelot 
and  Vielle,  and  particularly  by  Mallard  and  Le  Chatelier. 
Students  are  referred  to  the  monograph  of  the  latter  experimenteis  * 
for  details  of  method  and  result  under  this  and  the  following 
sections.  To  determine  the  temperature  of  inflammation,  mix- 
tures were  admitted  rapidly  into  a  chamber  previously  heated 

*  Under  the  title  "  Recherches  Experimentales  et  Theoriques  sur  la  Com- 
bustion des  Melanges  Gazeux  Explosifs,"  par  MM.  Mallard  et  Le  Chatelier, 
Xng^nieurs  au  Corps  des  Mines.  Commission  de  Grison,  1883. 


524  THE   GAS- ENGINE. 

to  a  known  temperature.  It  is  then  observed  whether  the  mix- 
ture unites  or  not,  and  two  limits  are  observed  between  which 
the  temperature  of  ignition  must  lie.  Testing  with  hydrogen, 
carbonic  oxide,  and  marsh-gas,  the  limits  were  found  to  be  for 
all  mixtures: 

H 5I7-595°>  mixed  with  air,  O  and  CO2. 

CO 630-725°,  mixed  with  air,  O  and  CO2. 

C2H4 640-760°,  mixed  with  air  and  O. 

Experiments  on  slow  combustion  show  a  discontinuity  be- 
tween  it  and  that  accompanied  by  light  and  heat  changes. 
In  general  the  temperature  of  inflammation  can  be  fixed  at 

555°  for  explosive  mixtures  of  H  and  O. 
655°  "          "  "        "  CO  and  O. 

656°  "          "  "        "  C2H4andO. 

The  addition  to  explosive  gas  of  even  a  considerable  volume 
of  inert  gas  modifies  little  or  not  at  all  the  temperature  of  in- 
flammation. 

However,  with  mixtures  of  CO  and  O  the  addition  of  a  notable 
quantity  of  CO2  seems  to  elevate  that  temperature  to  a  sensible 
degree.  One  volume  of  CO2  added  to  explosive  mixtures  CO+  O 
raises  the  temperature  from  655°  to  700°. 

For  mixtures  in  which  H  and  O  are  the  elements,  the  com- 
bustion takes  place  as  soon  as  the  temperature  of  inflammation 
is  reached.  It  is  entirely  otherwise  for  marsh-gas,  which  may  be 
likened  to  fire-damp.  The  mixtures  formed  by  this  gas  with  air 
or  oxygen  do  not  burn  except  after  having  been  brought  to  a  tem- 
perature equal  or  superior  to  that  of  inflammation  and  kept  there 
for  perhaps  ten  seconds.  The  retarding  of  inflammation  in- 
creases with  difference  of  temperature  of  gas  and  that  of  inflamma- 
tion, and  with  the  increase  of  the  proportion  of  inert  gas.  This 
latter  reason  explains  why,  according  to  Davy,  a  bar  of  red-hot 
iron,  though  above  650°,  will  not  ignite  a  mixture  of  fire-damp. 
By  opposing  circulation  one  may  easily  provoke  inflammation, 


TESTS  ON  EXPLOSIVE  MIXTURES.  525 

because  when  it  circulates  freely  the  gas  does  not  remain  long 
enough  exposed  to  the  temperature  of  inflammation. 

227.  The  Rate  of  Propagation  of  Flame. — Previous  to  Mallard 
and  Le  Chatelier  this  question  had  been  attacked  by  Sir  Humphry 
Davy  and  by  MM.  Bunsen,  Schloesing  and  De  Mondesir, 
Fonesca  and  Gouy,  Berthelot  and  Vielle. 

A  summary  of  the  work  by  Mallard  and  Le  Chatelier  on 
propagation  of  inflammation  brings  out  the  following  facts: 

There  are  two  modes  of  propagation:  (i)  normal,  which  is 
that  by  conductivity,  and  (2)  explosive,  which  takes  place  by 
the  transmission  through  the  mixture  of  a  pressure  sufficiently 
high  to  cause  propagation  by  explosive  wave.  These  corre- 
spond to  deflagration  and  explosion  of  dynamite,  etc.  Each  has 
a  fixed  velocity  for  a  given  mixture  at  a  given  pressure. 

The  phenomena  of  the  explosive  wave  are  of  notable  interest 
and  will  be  referred  to  in  the  next  paragraph.  The  rate  of  normal 
propagation,  denoted  by  R,  never  exceeds  20  m.  per  sec. 

For  H  and  air  the  maximum  is  4.30  m.  per  sec.  for  a  40  per 
cent  H,  i.e.,  an  excess  (30  per  cent). 

For  C2H4  and  air  the  maximum  is  0.62  m.  per  sec.  for  a  12.2 
per  cent,  i.e.,  an  excess  (9.4  per  cent). 

For  illuminating-gas  and  air  the  maximum  is  1.25  m.  per  sec. 
for  a  17.0  per  cent,  i.e.,  an  excess  (15  per  cent). 

For  CO  and  O  and  air  the  maximum  is  2.00  m.  per  sec. 
always. 

R  increases  with  7,  the  rate  of  ignition,  and  when  the  tube  is 
large  is  independent  of  diameter,  but  a  tube  small  enough  may 
cause  extinction. 

Agitation  increases  R.  Combustion  in  the  tube  with  slow  R 
sets  up  oscillation  which  may  cause  extinction. 

When  for  any  reason  of  vibration  or  explosion  of  burnt  gas 
the  pressure  transmitted  to  a  layer  next  is  equal  to  that  which 
would  elevate  it  to  the  temperature  of  inflammation,  the  com- 
bustion propagates  with  the  same  velocity  as  the  compressive 
wave,  resulting  in  the  explosive  wave. 


526  THE  GAS-ENGINE. 

228.  The  Propagation  of  an  Explosive  Wave.  —  Messrs. 
Schloesing  and  De  Mondesir,  in  experiments  upon  ignition  and 
propagation  of  flame  in  a  long  glass  tube  open  at  one  end  and 
closed  at  the  other,  noticed  that  in  mixtures  in  which  the  normal 
rate  of  propagation  was  slow  it  was  possible  to  produce  true 
explosions  of  instantaneous  character.  These  explosive  pro- 
jections of  flame  seemed  to  be  the  result  of  interior  agitation  in 
the  mixture,  probably  of  a  vibratory  order,  and  similar  to  the 
result  of  projecting  a  jet  of  gas  at  high  velocity  into  a  mass  of 
gas  at  rest.  If  these  agitations  are  produced  in  any  given  case, 
the  usual  rate  of  propagation  becomes  disturbed,  and  pressures 
will  result  much  in  excess  of  the  expected  pressure.  The  causes 
of  such  abnormal  propagations  as  are  traceable  to  disturbance  of 
the  mixture  will  be  present : 

1.  When  different  parts  of  the  mixture  are  of  differing  densi- 
ties from  temperature  or  other  causes; 

2.  When  an  expansion  caused  by  the  increase  in  volume  of  a 
part  of  the  gas  on  burning  produces  local  compressions  which 
are  not  instantly  relieved  by  the  yielding  of  the  mobile  mass. 
Pockets  or  confined  volumes  are  particularly  subject  to  this. 

3.  When  a  vibratory  motion  in  the  gas  itself  results  from  the 
process  of  propagation.     When  this  synchronizes  with  the  normal 
propagation  rate  the  combination  may  result  in  a  superposition 
of  pressures  beyond  that  which  the  confining  vessel  can  with- 
stand. 

Messrs.  Berthelot  and  Vielle  carried  observation  of  these 
phenomena  farther,  but  the  most  conclusive  demonstrations  are 
those  of  MM.  Mallard  and  Le  Chatelier.  These  investigators 
not  only  produced  the  phenomena,  but  devised  a  photographic  auto- 
matic record  of  the  explosive  process  to  which  Berthelot  and  Vielle 
had  given  the  name  of  "explosive  wave"  when  generated  in  a 
tube.  The  pressures  caused  by  this  wave  in  tubes  of  glass  of  two 
millimetres  in  thickness  were  sufficient  to  reduce  them  to  powder, 
although  previously  tested  by  static  pressures  above  150  pounds 
to  the  square  inch.  The  pressure  was  sufficiently  instantaneous 


TESTS  ON  EXPLOSIVE  MIXTURES.  527 

in  character  to  behave  as  high  explosives  do,  in  that  a  discharge 
in  a  funnel,  immersed  in  water,  so  that  only  the  resistance  due 
to  the  inertia  of  the  latter  opposed  free  escape  of  the  pressure, 
yet  resulted  in  shivering  the  funnel  to  atoms.  As  observed  by 
Mallard  and  Le  Chatelier,  and  graphically  recorded,  the  action 
might  be  analyzed  into  four  phases,  which  might  be  successive, 
or  which  might  overlap,  or  of  which  one  or  more  might  not  occur. 
The  first  phase  was  the  non-concussive  propagation;  the  second 
the  ampler  vibratory  motion;  this  passed  into  the  third  or  deto- 
nating stage,  when  the  amplitude  of  vibration  was  a  maximum; 
and  the  fourth  stage  was  an  extinction  of  the  flame  before  com- 
plete combustion  of  the  whole  mixture  had  been  effected  either 
by  a  dissociation  phenomenon  or  from  some  other  cause. 

A  most  interesting  practical  investigation  at  Columbia  Uni- 
versity has  shown  that  these  phenomena  can  easily  be  manifested 
in  explosive  engines.  The  presence  in  the  combustion-chamber 
volume  of  pockets  in  which  explosive  mixtures  can  be  imprisoned 
with  narrow  channels  connecting  them  may  easily  cause  the 
vibratory  movement  referred  to  above.  The  first  ignition  pressure 
receives  a  distinct  secondary  impulse,  and  the  whole  mass  be- 
comes subject  to  pressure  waves  in  motion.  This  can  be  made 
to  show  itself  on  the  indicator-card  of  the  engine,  first  in  pressure 
much  above  the  normal,  and  secondly  in  a  wave  effect  on  the 
expansion  line  far  above  any  record  which  can  be  attributed  to 
inertia  of  the  reciprocating  weights  of  the  indicator  itself.  This 
can  be  proved  by  the  simple  test  of  adding  to  a  normal  engine 
an  extra  volume  to  its  clearance,  connected  thereto  by  a  narrow 
neck  of  pipe,  and  connecting  the  indicator  to  this  second  or 
supplementary  volume.  The  indicator  which  gave  normal 
cards  before  the  addition  of  the  supplementary  chamber  gave 
strong  vibratory  lines  after  the.  connection  of  the  chamber  was 
made,  ail  other  conditions  being  the  same.  The  piston  com- 
pressions may  produce  similar  vibrations,  and,  in  the  case  of 
advanced  sparking  adjustment,  superpose  the  ignition  pressure 
upon  the  vibration  effect,  making  the  engine  thump  badly,  and 


528  THE  GAS-ENGINE. 

perhaps  even  stopping  it  before  the  end  of  the  stroke  is 
reached. 

It  is  apparent,  therefore,  that  the  cylinder  casting  must  be 
strong  enough  to  withstand  not  only  the  computed  or  normal 
ignition  pressure,  but  must  be  able  to  resist  the  very  much  higher 
stress  which  the  explosive  wave  may  cause.  The  clearance 
must  also  be  free  from  subdivisions,  from  which  vibratory  effect 
can  be  started.  The  results  of  the  explosive  wave  action  may  be 
compared  to  those  due  to  water-hammer  in  steam-pipes,  and  the 
presence  of  excess  of  water  in  steam-engine  cylinders  which  are 
not  fitted  with  relief- valves. 

229.  Concluding  Comment. — It  will  be  apparent  from  the  fore- 
going review  of  work  already  begun  and  carried  forward  in  this 
field  that  it  is  at  this  point  that  the  student  and  laboratory  in- 
vestigator touch  most  vitally  upon  the  problems  of  the  actual 
designer  of  the  gas-engine.  It  is  the  knowledge  of  the  formation 
of  these  explosive  mixtures,  their  behavior  in  the  cylinder  under 
the  conditions  there  prevailing,  and  the  constants  which  are  to  be 
introduced  as  coefficients  in  formulae  and  computations,  which 
make  this  subject  and  its  possibilities  particularly  inviting.  It 
is  to  be  hoped  that  additions  to  the  stock  of  knowledge  in  existence 
and  on  record  along  these  lines  may  be  made  both  rapidly  and 
to  great  extent. 


CHAPTER  XX. 

COSTS  OF  OPERATION. 

230.  Introductory.  —  There  are  difficulties  inseparable  at 
present  from  an  effort  to  give  satisfactory  discussion  of  the 
economic  aspect  of  the  internal  combustion  motor.  Among 
these  are: 

i.  The  meagerness  of  reliable  data  in  unprejudiced  hands. 
In  America,  while  the  building  of  small  motors  has  been  in 
progress  for  some  time,  the  operation  of  large  units  is  quite 
new.  The  builders  have  much  accumulated  information,  but 
if  it  is  favorable  to  their  product  they  prefer  to  retain  the  facts 
in  their  possession  with  a  view  to  making  use  of  them  in 
furthering  their  sales:  and  if  unfavorable  to  them  in  competi- 
tion, they  prefer  to  retain  their  acquired  knowledge  lest  it  be  used 
against  them.  In  Europe,  the  industry  is  older,  and  the  legis- 
lative requirements  frequently  compel  publication  of  costs  as 
features  of  municipal  ownership  or  control  of  public  service 
power  plants.  Hence  there  are  data  available  there.  But  two 
difficulties  appear  here  and  should  be  guarded  against.  The  one 
is  the  difference  in  social  and  labor  and  fuel  conditions  on  the  two 
sides  of  the  Atlantic,  with  their  effects  upon  all  economic  ques- 
tions; and  the  other  is  the  fact  that  municipal  control  and 
management  (whether  complicated  or  not  with  municipal  owner- 
ship) has  always  up-to-date  managed  its  technical  and  engineer- 
ing matters  without  proper  attention  to  upkeep  and  renewal.  In 
the  early  days  of  the  plant  too  little  is  set  aside  for  proper  main- 
tenance, in  order  to  make  a  good  showing;  and  as  the  result  of 
this  the  cost  of  producing  the  power  unit  becomes  too  great  in  the 
later  years  after  the  plant  has  run  down.  Both  causes  throw 

529 


53^  THE  GAS-ENGINE. 

suspicion  upon  the  figures  in  the  reports,  and  lessen  their  value 
as  guides. 

2.  The  figures  of  cost,  which  serve  as  basis  for  comparison,  are 
changing  continually.     The  internal  combustion  engine  enters 
the  power  producing  field  as  a  rival  or  a  supplanter  of  the  steam 
engine.     The  elements  of  cost  of  the  latter  are,  therefore,  the 
usual  elements  of  comparison.     But  the  cost  of  steam  power  is 
not  a  stationary  standard:  new  designs  or  new  processes  con- 
tinually advance  beyond  the  older  standards  and  compel  new 
values  to  be  considered.     Fuel  consumptions  and  fuel  costs  are 
varying  bases,  and  facts  and  figures  of  any  year  are  superseded 
and  become  out  of  date. 

3.  Fuel  economy  and  fuel  costs  are  not  the  only  basis  upon 
which  selection  of  a  motor  can  be  or  should  be  made.     In  the 
motor  car  for  example,  when  used  for  pleasure  purposes  by  un- 
trained operators,  fuel  expense   may  be  entirely  secondary  to 
other  considerations,  such  as  flexibility,  silence,  absence  of  shock 
or  jar  and  simplicity  of  detail. 

In  the  figures  which  follow,  therefore,  the  changeable  character 
of  the  values  used  must  not  be  lost  sight  of:  nor  the  possible 
inapplicability  of  the  foreign  figures  to  American  conditions  of 
private  ownership  control. 

4.  It  should  also  be  remembered  that  in  many  industrial  plants, 
the  heat  of  the  exhaust  steam  from  the  engines  is  used  either  in 
processes  or  in  heating  the  buildings  in  winter.     Costs  of  power 
in  this  case  should  not  be  charged  with  the  price  of  such  fuel  or 
heat  units  as  are  applied  to  heating.     If  gas  engines  were  used, 
steam  would  have  to  be  supplied  in  addition;  or  it  may  happen 
that  in  effect  the  power  fuel  costs  nothing,  and  the  engine  is  a 
sort  of  reducing  valve  between  the  boilers  and  the  heating  coils. 

5.  As  against  this  may  be  offset  the  advantage  offered  by  the 
internal    combustion    engine    as    respects    subdivided    units    of 
power  in  different  buildings  or  parts  of  a  plant.     The  small 
steam  engine  is  not  so  economical  or  efficient  as  the  large  unit: 
the  gas  engine  does  not  suffer  from  this  limitation.    Hence  the 


COSTS  OF  OPERATION.  53, 

gas  may  be  made  by  a  central  producer,  and  distributed  by 
mains  to  a  large  number  of  small  gas-engine  units  for  use  when 
and  where  required.  To  distribute  steam  from  such  a  central 
station  is  wasteful  of  heat  in  transmission  and  the  small  steam 
unit  is  wasteful.  In  gas  distribution  there  is  little  waste,  and  the 
small  unit  nearly  as  economical  as  the  large  one.  Electrical 
subdivision  is  expensive  in  first  cost,  and  the  loss  of  efficiency  in 
the  double  transformation  from  mechanical  into  electrical  energy 
and  then  back  again  entails  more  loss  than  that  of  the  combined 
producer  piping  and  gas-engine.  The  gas  can  also  be  taken 
from  the  producer  pipes  and  burned  in  suitable  stoves  for  heat- 
ing. In  some  climates  the  jacket  water  can  be  used  in  hot  water 
circulating  coils  as  heat  radiators  for  warming  the  building,  and 
the  economy  of  the  gas-engine  be  greatly  enhanced. 

Great  caution  should,  therefore,  be  exercised  in  generalizing 
from  the  limited  number  of  particular  instances  referred  to  in 
this  chapter.  Many  more  will  be  required  before  general  con- 
clusions should  be  enunciated,  and  the  question  in  each  case 
should  be  studied  from  all  of  its  aspects. 

231.  The  Elements  of  Cost.  —  The  elements  which  go  to 
make  up  the  cost  of  power  in  gas-engines  are  essentially  the  same 
as  in  all  power  generating  stations.  The  first  and  obvious 
division  is  into  the  first  cost  and  the  operating  cost;  but  as  the 
money  to  pay  for  the  first  cost  of  the  installation  in  buildings  and 
machinery  will  either  be  borrowed  directly  or  will  be  withdrawn 
from  other  investments  in  which  it  is  earning  the  usual  interest,  it 
is  easier  to  put  this  yearly  interest  as  an  element  of  the  operating 
cost.  It  is  generally  true  that  money  intelligently  spent  in  good 
engineering  in  the  first  cost  reduces  the  operating  expense -more 
than  the  increased  interest  on  such  first  cost,  by  diminishing 
repairs  and  renewals. 

The  fuel  energy  may  be  bought  in  the  form  of  gas  from  outside 
makers,  or  it  may  be  made  from  the  raw  material  in  the  plant 
itself.  In  the  former  case  the  buyer  pays  to  the  seller  a  price 
for  fuel  which  covers  the  latter's  expenditure  in  manufacturing, 


532  THE   GAS-ENGINE. 

and  his  interest  on  the  plant  used  in  distributing  together  with 
the  usual  profit  in  his  business.  If  he  makes  the  gas  himself  he 
pays  for  these  same  elements  of  cost,  but  usually  less  than  he 
pays  to  the  outsider,  and  the  profits  inure  to  himself.  If  the  gas 
generating  or  producing  plant  within  his  own  walls  is  large 
enough  to  derive  the  advantages  of  large  scale  manufacture,  it 
will  be  cheaper  to  make  his  own  gas  from  intramural  producers. 
If  on  the  other  hand  the  demand  for  gas  is  very  small,  so  that  it 
can  be  met  by  carbureters,  here  also  the  process  will  be  cheaper 
to  make  the  gas  as  the  engine  requires  and  not  to  depend  on 
outside  concerns.  While  on  general  principles  the  large  scale 
manufacture  will  be  the  cheaper,  yet  the  losses  in  leakage  and  the 
expense  of  distribution  of  the  gas  give  the  producer  and  especially 
the  suction  producer  a  very  great  opportunity  to  work  success- 
fully in  competition.  The  elements  of  cost  in  the  general  case 
will  therefore  be: 

i.  Interest  on  the  First  Cost.  —  If  the  cost  of  the  producer  is  to 
be  included,  the  gas  plant  is  about  the  same  as  the  steam  plant, 
less  the  chimney.  If  this  is  costly  in  the  competitive  steam  plant, 
or  is  equated  by  the  cost  of  a  mechanical  draft  outfit  of  engine 
and  fans,  the  gas  plant  comes  out  ahead.  In  large  installations 
the  individual  gas-engine  unit  is  not  so  large  as  yet  as  the  steam- 
driven  unit.  More  units  are,  therefore,  required  to  attain  the 
same  maximum  power.  Engineers  do  not  seem  inclined  to  re- 
commend single  electric  units  laiger  than  900  kilowatts  capacity 
per  cylinder-end  with  gas-engine  power  so  that  the  capital  invest- 
ment during  the  continuance  of  this  condition  will  average  about 
25  per  cent  greater  for  the  gas  plant  than  the  equivalent  steam 
plant.  If,  on  the  other  hand,  the  station  is  of  a  capacity  making 
comparison  of  units  possible  by  their  output,  the  space  occupied 
by  a  steam-engine  and  steam  generating  plant  being  called  100, 
the  space  for  the  gas-generators  and  engines  will  be  80.  The 
cost  of  buildings  will  be  as  70  to  60.  If  the  gas  is  delivered  from 
mains  from  without,  the  space  will  be  30  on  the  basis  of  100  for  the 
steam  plant,  and  the  cost  as  50  to  the  ratios  of  70  and  60  above. 


COSTS  OF  OPERATION.  533 

2.  Depreciation  and  Sinking  Fund.  —  The  moment  that  the 
machinery  and  buildings  have  been  paid  for,  they  are  second- 
hand articles  and  are  not  worth  what  was  paid  for  them.  They 
also  are  running  down  in  quality  by  use  and  wear  and  by  the 
process  of  becoming  obsolete  by  time.  Sound  financing  demands, 
therefore,  that  each  year  their  book  value  in  the  accounting  be 
diminished,  until  after  a  period  of  n  years  (to  be  fixed  by  the 
owners  and  investors)  their  value  shall  disappear  as  an  asset  on 
the  books.  This  period  may  be  the  same  or  shorter  than  that  at 
which  an  investment  of  new  machinery  will  have  to  be  made  if 
the  plant  is  to  continue  in  business;  and  at  the  end  of  this  time 
money  or  available  capital  should  be  in  bank  or  investment  to 
pay  for  this  renewal  without  impairing  the  capital  again  or  bring- 
ing in  new  subscribers.  The  depreciation  of  gas-engines  is 
greater  or  their  life  period  shorter  than  that  of  the  equivalent 
steam-engine,  by  reason  of  the  sudden  character  of  the  stresses, 
the  high  temperature  at  which  they  work,  the  difficulties  with 
dirty  gas  and  defective  lubrication  and  wear  of  the  valves.  Gas- 
engines  at  present  also  are  changing  type  and  undergoing  such 
rapid  improvement  that  they  become  old  in  a  shorter  time. 
The  depreciation  and  sinking  fund  factor  will  be  greater  in  a  gas- 
driven  than  in  the  equivalent  steam-driven  plant.  In  the  steam 
plant  it  is  usually  5-7  per  cent  or  is  based  on  a  presumption  of  life 
of  1 5-20  years.  In  the  gas-engine  plant  the  presumption  of  life 
is  nearer  10  years  or  even  as  low  as  eight  in  small  engines.  In 
larger,  it  will  be  12-15.  In  the  motor-car  for  pleasure  it  is 
rarely  over  three  or  even  two  years,  by  reason  of  the  hard  ser- 
vice, in  unskilled  hands  for  the  most  part,  and  also  from  the 
rapid  changes  in  design.  Th?  demand  for  lightness  of  weight 
induces  close  economy  in  computing  bearing  or  wearing  areas, 
with  consequent  shortened  life.  The  sinking  fund  for  toth 
machinery  and  plant  may  be  fixed  arbitrarily  by  a  determination 
to  pay  for  the  plant  in  so  many  years. 

3.   Renewals. — The    distinction  between  a   renewal   and   a 
repair  is  that  a  renewal  makes  that  part  as  good  as  when  first 


534  THE   GAS-ENGINE. 

put  in,  and  should,  therefore,  have  its  full  presumption  of  life 
counted  from  the  date  of  such  renewal.  A  repair  on  the  other 
hand  makes  good  only  to  the  degree  of  excellence  which  existed 
after  the  previous  wear  and  tear  had  taken  place.  Renewal  by 
installment  may  be  the  same  in  effect  as  expenditure  from  the 
sinking  fund,  giving  a  substantially  new  machine  when  these  have 
been  completed. 

4.  Repairs  and  Maintenances.  —  The  plant  may  be  allowed 
to  deteriorate  in  quality,  and  usually,  therefore,  also  in  economy, 
by  neglect  in  its  upkeep.     Leaky  piston-rings  and  valves,  lost 
motion  in  the  bearings,  due  to  cutting  and  wear,  produce  a  greater 
invasion  of  operating  economy  in  the  gas-engine  than  in  the  steam- 
engine,  particularly  the  compound  or  multiple  expansion  type  of 
the  latter.     Dirty  gas  and  deformations  by  heat,  by  reason  of 
defective  cooling  systems,  make  the  contact  surfaces  lose  their 
shape  and  pressure  and  fuel  leaks  away.     Repairs,  properly  so- 
called  as  distinguished  from  renewals,  ought  not  to  exceed  5  per 
cent  in  a  new  plant.     The  labor  of  the  employees  otherwise 
required  can  usually  be  relied  on  for  simple  repairs. 

5.  Fuel,  Oil  and  Supplies.  —  The  probable  fuel  expense  will 
be  treated  in  a  following  paragraph.     It  will  increase  with  the 
age  of  the  plant,  or  carelessness  in  maintenance,  whereby  pistons 
and  valves  grow  leaky.     More  fuel  is  required  under  these  con- 
ditions to  furnish  the  same  power.     The  use  of  poor  oil  or  that 
ill  chosen  for  the  conditions  prevents  the  piston-rings  from  per- 
forming their  functions,  and  by  its  presence  as  gum  causes  exces- 
sive wear  and  leakage.     It  is  almost  a  generalization  from  the 
facts  of  public  or  municipal  control  of  gas-driven  plants,  that 
under  their  conditions  of  management  where  the  responsibility 
for  the  capital  investment  is  remote  or  is  a  community  matter, 
the  fuel  or  operating  expense  is  greater  before  long  than  in  the 
private  plant  of  the  same  age.     These  conditions  seem  due  to 
carelessness    or    mistaken    economy,    whose    consequence    is   a 
lowered  physical  condition  of  the  plant,  and,  therefore,  a  greater 
fuel  waste  or  demand. 


COSTS    OF  OPERATION.  535 

6.  Labor.  —  With   mechanical   handling  of  the   fuel   to   the 
producers,  the  labor  requirement  in  the  boiler-room  of  the  parallel 
steam  plant   will   be  about   the   same.     With   hand-firing,   the 
producer  plant   is   the  cheaper  to  operate.     The   engine-room 
price  will  be  the  same  for  the  two  cases. 

7.  Water.  —  The  cost  of  the  cooling  water  will  be  determined 
by  the  source  from  which  it  comes.     If  city  water  from  the  mains 
is  used,  the  water  tax  in  a  large  plant  will  be  a  considerable  sum. 
Near  a  flowing  river  or  large  pond  the  cost  will  be  only  that  of  the 
interest  and  operation  cost  of  the  circulating  apparatus  less  the 
return  from  any  other  uses  to  which  the  water  may  be  put. 
Where  water  is  scarce,  and  impounding  reservoirs  and  cooling 
towers  or  other  apparatus  must  be  installed,  the  cost  of  these 
adjuncts  may  appear  either  in  the  elements  of  first  cost  in  the 
accounting  or  may  be  charged  to  the  water  cost.     Where  air- 
cooling  can  give  satisfactory  results,  the  water  expense  is  elimi- 
nated, but  much  more  massive  apparatus  in  fans  and  ducts  is 
required  for  efficient  cooling,  and  in  large  plants,   where  the 
quantity  of  heat  in  the  cylinder  per  ignition  becomes  large,  the 
air-cooling  system  has  not  as  yet  been  found  satisfactory. 

8.  Insurance.  —  The  charge  for  insurance  is  often  treated  as 
an  overhead  or  office  account,  detached  from  the  engineering 
factors ;  but  the  design  and  conception  of  the  plant  may  materially 
affect  the  rate.     If  the  fuel  used  is  gas  from  the  city  mains  no 
effect  is  produced  upon  the  rate,  but  the  requirement  is  made  that 
the  exhaust  pipe  be  carried  to  the  open  air  in  full  metallic  strength, 
and  not  simply  led  into  a  brick  or  masonry  flue.     This  is  to 
diminish  fire-hazard  from  possible  flaming  explosions  in  such 
flue.       If  the  fuel  is  liquid  gasoline  or  kerosene,  the  fire-laws 
may  limit  the  quantity  on  storage  at  one  time,  or  may  compel 
storage  in  an  outside  building  or  in  a  vault  underground  with 
special  construction  or  safe  guards  and  consequent  installation 
expenses.     If  the  fuel  is  to  be  made  from  producers,  the  insurance 
requirements  may  be  made  practically  prohibitory  in  some  cities, 
and  their  presence  vitiate  all  insurance  on  the  rest  of  the  plant. 


536 


THE  GAS-ENGINE. 


If  the  producer  can  be  isolated,  it  may  be  operated  without 
insurance.  The  normal  view  would  make  the  producer  insurance 
the  same  as  the  boiler-plant  rate.  The  combustible  character 
of  the  gas  made  in  the  producer  should  offset  the  higher  tem- 
perature of  the  boiler  furnace  and  its  gases,  and  the  danger  from 
the  rupture  of  the  steam-reservoir  under  pressure. 

9.  Overhead  Charges.  —  These  are  the  elements  of  non- 
productive expense  of  the  plant  which  do  not  appear  directly 
as  elements  of  the  operating  or  as  factors  of  the  output.  Salaiies 
not  chargeable  to  power  production,  the  office  expenses,  taxes, 
rental,  interest,  royalties,  fees  and  any  other  elements  not  group- 
able  under  one  of  the  preceding  headings,  will  be  included  under 
this  heading. 

In  the  following  tables,  the  capital  investment  and  the 
operating  expense  from  various  British  and  continental  reports 
are  brought  together,  the  British  pound  being  equated  to  five 
dollars,  and  the  English  penny  to  two  cents  in  the  American 
currency.  The  English  Board  of  Trade  Unit,  is  the  kilowatt 

horse  power  per  hour. 


per   hour,  equivalent  to  —  -  = 

746 


COST  OF  PRODUCER  AND  KILOWATT. 


Capacity  of 
Station  in 
Kilowatts. 

Cost  of  Gas 
Producers 
Dollars. 

Capacity  of 
P.roducers 
Cu  ft.  Per  Hour. 

Cost  per  Kilo- 
watt for  Plant 
Dollars. 

Cost  per  Kilo- 
watt Producers 
and  Engines 
Dollars. 

Source  or 
Authority. 

22O 
600 

14,400 
24,000 

I3>320 
24,200 

... 

65* 

40* 

Dawson 
Dawson 

300 

235 
170 

3>725 

... 

364 
404 
1  80 

126 
122 

i3St      ' 

Lausanne 
Zurich 
Krone 

*  Producers  only. 


f  Includes  generators. 


COSTS  OF  OPERATION. 


537 


COST  OF  400  H.  P.  GERMAN  ENGINES  (KORTING). 


Item. 

Cost  Dollars. 

Street  Gas. 

Producer  Gas. 

Gets  Plant  and  Erection 

12,725 
75° 
500 
300 
300 
400 

4125 
12,800 
625 
250 

300 
600 

* 

Engine  and  Bolts                                          

Pioing                                                     

Starter                       

Total                        

14,970 
IOO 

18,700 
I2O 

Cost  per  Kilowatt  Exclusive  of  Buildings        

OPERATING  COSTS  (CENTS  PER  KILOWATT  HOUR). 


Location,  Source  or  Authority. 


Item. 

Laus- 
anne 
1899. 

Rugby 
1898. 

Leyton 
1898. 

Orleans* 
St.  Ry. 
1899. 

Linden 
1899. 

Zurich 
1899-* 

Zurich 
1899* 

Fuel      

0.038 

I  .420 

I  .0228 

<;oo 

I    080 

<88 

068 

Oil  and  Supplies      

.074 

.4<O 

.1866 

OQ4 

312 

04.4. 

I  ^O 

Wages  and  Salaries  
Maintenance  and  Repairs 
Water                      

•37° 
.184 
.066 

I  .  710 

.288 

2  .  4642 
.0718 

.600 

.400 

2.664 
.360 

.268 
.230 
O^2 

4-50 
.230 

1  08 

Sundries                   

.024 

642 

General  Expense  
Cost  per  Kilowatt      .... 

.642 

2     373 

2.084 
r    Qira 

I  .  0892 

4   8346 

I    640 

5O4O 

.154 

2    060 

Cost  of  Fuel  per  Ton..  . 

$6-$7. 

$5.40 

$6.  -$6.50 

*  Does  not  include  interest  or  sinking  fund. 

If  these  be  reduced  to  percentages  of  the  fuel  cost  as  100  per 
cent,  the  following  table  will  result,  although  its  applicability  to 
American  conditions  is  greatly  lessened  by  the  exceptionally  high 
fuel  cost. 


538  THE   GAS-ENGINE. 

RELATIVE  COST  OF  ITEMS  TO  FUEL  COST  IN  PERCENTAGES. 


Item. 

Laus- 
anne. 

Rugby 

Leyton. 

Orleans. 

Linden. 

Zurich 

Zurich. 

Fuel 

IOO 

IOO 

Supplies 

7 

•3  I 

18 

18 

Wages 

Of 

I2O 

22  1 

6^ 

Ag 

•a 

Maintenance  
Water  .  .              .... 

19 

6 

20 

*-*J 

7 

80 

37 

4D 

37 
6 

22 
IO 

Sundries 

2 

General  Exnense  .  . 

68 

146 

TO  A 

TC 

The  differing  methods  of  accounting  must  also  be  recognized 
:as  making  a  general  comparison  or  generalization  impossible 
and  erroneous. 

COST  OF  KILOWATT  PER  HOUR  IN  CENTS. 


Cost  of  Kilowatt  per  hour  in  cents. 


Gas-Engine  Plant. 

Steam-Engine  Plant. 

Fuel  

8 

Oil  and  Supplies  

"             01       "   0    76 

\Vages  and  Salaries 

"                  ~AQ    "    ,,     AA,, 

.^Maintenance 

.06        3  .  20 

Total  

^•^00       y  •  ou 

A  comparative  table  of  the  cost  of  the  kilowatt  per  hour  in 
steam  plants  and  in  gas-driven  plants  presents  the  following 
figures : 

FUEL  COST  OF  POWER. 


Fuel  and  type  of  Plant. 

Fuel  required 
per  horse- 
power per 
hour. 

British 
thermal 
units  re- 
quired per 
horse-power 
hour. 

Thermal 
efficien- 
cy. 

Cost  of  fuel. 

Cost  of 
fuel  per 
kilowatt 
per  hour. 

Anthracite  coal  : 
Large  steam  plant    . 

2  pounds.  .   . 

Per  cent 

Cents. 

Do  

2  pounds 

.764 

Small  steam  plant.  . 

7  pounds,  .   . 

2* 

2.50  per  ton    

1-34 

Do  

7  pounds.   .   . 

3 

6  25  per  ton 

2  048 

Producer  gas  plant 

18 

.188 

Do  

ii  pounds 

14,000 

18 

6  25  per  ton        

•415 

Do            .... 

14,0 

Do            

* 
.764 

Illuminating  gas  
Crude  oil 

24  cubic  feet  . 

12,000 

20 

1 

i  .00  per   i  ,000  cubic  feet 

2.048 
.911 

1.4  p  n     .... 

2.278 

Do 

4-5S6 

Alcohol. 

6.700 

Do... 

<ZIQ 

.40  per  gallon  

8.978 

Efficiency  of  alcohol  is  assumed  to  be  the  same  as  that  of  gasoline  for  identical  conditions  of  use. 


COSTS  OF  OPERATION.  539 

This  confirms  qualitatively  the  usual  central  station  figure  for 
steam  plants  in  America,  where  small  consumers  pay  at  a  rate 
of  five  cents  per  kilowatt  hour,  and  larger  users  at  a  much  lower 
rate,  still  leaving  a  margin  for  overhead  charges  and  profit  in  the 
business. 

232.  The  Fuel  Cost  and  Guarantee.  —  The  preceding  para- 
graph has  been  intended  to  call  attention  to  the  factors  to  be 
studied  and  evaluated  when  the  general  question  of  the  use  of  the 
gas-engine  is  under  consideration.  When  this  has  been  settled, 
and  the  matter  under  advisement  is  one  between  a  buyer  and  the 
vendor  of  a  particular  engine,  the  broader  elements  come  less 
into  prominence,  and  the  question  of  fuel  cost  becomes  the  para- 
mount one.  The  design,  the  generous  bearing  and  wearing 
areas,  the  facility  for  repair  and  adjustment  are  all  factors 
in  reducing  the  operating  expense  and  should  be  carefully  con- 
sidered in  deciding  on  competing  claims.  But  they  are  more 
remote  than  the  fuel  cost,  and  are  less  definitely  predicable. 
Hence  the  output  per  fuel  unit  is  the  most  usual  and  frequent  cost 
unit  in  use.  In  Chapter  II  in  general,  and  in  paragraphs  29,  40, 
46,  and  47  in  particular,  the  basis  for  theoretical  and  actual  fuel- 
consumption  for  brake  horse-power  with  a  given  fuel  have  been 
referred  to.  An  English  guarantee,  based  on  gas  made  in  a 
Dawson  producer  (paragraph  24,  25),  calorific  power  of  12,825 
B.T.U.  per  pound  higher  value,  was  a  brake  horse-power  on  85 
cubic  feet  of  gas  per  hour,  when  it  ran  145  B.T.U.  per  cubic 
foot.  A  very  common  American  guarantee  in  larger  plants, 
developing  1000  H.P.  is  to  give  one  brake  horse-power  on  one 
pound  of  coal  gasified,  provided  the  gas  runs  at  11,000  B.T.U. 
per  pound. 

In  the  last  reduction,  however,  the  final  arbitrament  will  be 
the  heat  units  (or  the  foot-pounds)  secured  by  the  purchaser  for 
dollar  expended  to  buy  fuel.  If  this  be  conceded,  then  it  will 
be  apparent  that  the  liquid  fuel  motors  are  to  be  preferred  to  the 
coal  users  only  where  reasons  of  convenience,  manageability, 
mechanical  or  automatic  supply  of  fuel  or  other  practical  reasons 


540 


THE  GAS-ENGINE. 


outweigh  the  purely  financial  aspect  of  the  cost  of  the  fuel  per 
pound.  Repeating  the  data  of  Chapter  II,  it  will  be  apparent 
from  the  following  table  of  calorific  powers  and  prices  per  unit, 
that  the  heat  units  for  a  dollar,  or  the  horse-power  per  hour,  bear 
the  ratios  there  stated.  The  H.P.  column  is  derived  from  the 
B.T.U.  by  dividing  the  latter  by  2545  which  is  the  B.  T.  U.  per 


H.P.   per  hour  since 
to  be  100  per  cent. 


778 


X  60  =  2545,  assuming  efficiency 


HEAT  UNITS  PER  DOLLAR,  AND  HORSE  POWER  PER  HOUR. 


Horse 

Cost    of 

Power 

Actual 
Effi- 

Fuel per 

Fuel. 

Price  in  Dollars. 

Calorific  Power 
per  Unit. 

Heat  Units 
for  a  Dollar. 

Hour 

ciency 
Proba- 

Horse 
Power 

per 
Dollar 

ble  in 

per 
Hour  in 

E  =100 

percent 

Cents. 

Small  anthra- 

cites   

2  .  50  per  ton 

12,500  per  Ib. 

10,000,000 

3Q2Q 

10 

O.2  5 

Large  anthra- 

OV   J 

***  D 

cites  

6.25  per  ton 

14,000  per  Ib. 

4,500,000 

I7l8 

10 

°-57 

City  Gas  .   .  . 

i  .00  per  looocu.  ft. 

500  per  cu.  ft. 

500,000 

196 

20 

2.  2O 

Natural  Gas. 

.  10  per  1000  cu.  ft. 

1000  per  cu.  ft. 

10,000,000 

3929 

15 

0.16 

Crude  Oil  .  . 

.04  per  gallon 

2  1,  ooo  per  Ib. 

1,200,000 

471 

10 

0.68 

Gasoline  .    .  . 

.  10  per  gallon 

18,000  per  Ib. 

1,200,000 

471 

I9 

1.14 

Gasoline  .    .  . 

.  25  per  gallon 

do. 

480,000 

1  88 

J9 

2.83 

Kerosene 

.  10  per  gallon 

20,000  per  Ib. 

I,2OO,OOO 

471 

J9 

J-^ 

Kerosene.    .  . 

.30  per  gallon 

20,000  per  Ib. 

400,000 

i57 

J9 

5.00 

Alcohol  .... 

.30  per  gallon 

13,500  per  Ib. 

270,000 

106 

19 

5.00 

The  fifth  column  can  only  be  made  of  practical  significance  and 
use  by  multiplying  its  results  by  the  corresponding  actual  value 
of  the  efficiency  of  the  heat  when  transformed  into  mechanical 
work  in  the  appropriate  motor  apparatus.  For  example,  if 
the  large  steam  plant  using  poor  or  cheap  coal  gives  a  horse-power 
on  two  pounds  of  coal  per  hour,  or  on  25,000  B.T.U.  per  hour, 


it  attains  an  efficiency  of 


=  .10  or  ten  per  cent.     If  on  the 


25,000 

other  hand  the  more  usual  figure  for  small  plants  is  taken,  and 
the  consumption  per  brake  horse  power  approaches  seven  pounds, 
then  the  heat  units  rise  to  100,000  per  hour  and  the  efficiency 


COSTS  OF  OPERATION.  541 

drops  to  — •***   •  =  o.2S  or  2\  per  cent.    With  the  internal  com- 
100,000 

bustion  engine,  however,  the  discussion  in  paragraphs  47  and  203 
indicate  that  the  efficiency  may  rise  to  20  per  cent.  Hence  the 
results  in  columns  6  and  7  of  the  table  show  the  application 
of  these  principles  to  a  cost  comparison  of  the  differing  motors 
using  the  various  fuels.  From  this  the  fuel  cost  is  deducible  in 
any  given  case;  regard  being  paid  to  any  conditions  affecting 
the  applicability  of  the  assumed  efficiency  ratio  to  the  case  in 
hand. 


CHAPTER   XXI. 
CONCLUSION. 

.240.  Historical  Summary. — The  treatment  in  the  foregoing 
chapters  has  been  intentionally  free  from  reference  in  detail  to 
the  steps  in  the  transition  from  the  early  beginnings  to  the  present 
state  of  the  art.  This  was  done  first  because  to  have  done  other- 
wise would  have  been  to  turn  aside  from  the  main  purpose,  and 
secondly  because  this  descriptive  work  has  been  so  thoroughly 
done  by  others  in  previous  treatises.  Those  interested  may 
be  referred  particularly  to  the  work  of  Dugald  Clerk,  Bryan 
Donkin,  and  Wm.  Norris  in  England,  and  Gardner  D.  Hiscox 
in  America,  referred  to  in  the  next  section.  The  dates  of  im- 
portant patents  may  also  be  found  from  the  very  full  lists  in 
Clerk  and  Hiscox.  The  following  summary,  however,  will 
perhaps  be  found  useful: 

1794.  ROBERT  STREET  designs  a  pump  driven  by  explosion  of 
turpentine  vapor  below  the  motor  piston. 

1823.  SAMUEL  BROWN  designs  a  motor  to  operate  by  atmospheric 
pressure;  the  vacuum  tinder  the  piston  created  by  an 
explosive'  flame  to  expel  the  air  from  a  chamber,  and  a 
condensation  in  that  chamber  by  a  jet  of  water. 

1833.  L.  W.  WRIGHT.  Double-acting  motor,  supplied  with  gas 
and  air  by  separate  pumps,  and  using  a  water-jacket. 

1838.  WM.  BARNET.  Invents  compression  system  of  gas-motor. 
Ignites  with  flame. 

1855.  A.  V.  NEWTON.  Ignites  charges  by  contact  with  hot  metal 
surface. 

1857.  BARSANTI  and  MATTEUCCI  propose  a  free-piston  engine. 

1860.  LENOIR  of  Paris,  through  M.  Hippolyte  Marinoni,  builds 
a  double-acting  gas-engine  with  electric  ignition  by  jump- 
spark.  It  takes  mixture  by  aspiration  for  half-stroke, 

542 


THE  GAS-ENGINE.  543 

explodes  it  at  crank  position  90°  from  dead-centre,  and 
expands  during  the  econd  half -stroke.  Took  95  cubic 
feet  of  gas  per  H.P.  per  hour.  No  compression. 

1861.  F.  MILLION   proposes   compression   and   the  use  of  a  com- 

pression- or  combustion-chamber. 

1862.  ALPHONSE  BEAU  DE  ROCHAS,  Paris,  in  a  patent  of  Jan.   7 

and  a  later  pamphlet  urges  the  compression  four-stroke 
cycle  now  known  as  the  "Otto."  C.  W.  Siemens  of  Eng- 
land proposes  it  also. 

1865.  PIERRE  HUGON  injects  water  into  the  mixed  gases  in  the 
cylinder.  Consumption  made  85  cubic  feet  of  gas  per 
H.P.  per  hour. 

1867.  N.  A.  OTTO  and  EUGEN  LANGEN  exhibit  at  Paris  their  free- 
piston  atmospheric  engine,  using  44  cubic  feet  of  gas  per 
H.P.  per  hour. 

1872.  GEORGE  B.   BRAYTON  of  Philadelphia  designs  the  Bray  ton 

engine  with  constant-pressure  heating.  Called  Brayton's 
"Ready  Motor." 

1873.  JULIUS  HOCK  of  Vienna  patents  petroleum  engine. 

1876.  DR.  OTTO  brings  out  the  Otto  Silent  Gas-engine,  applying 
the  Beau  de  Rochas  cycle.  Gas  consumption  cut  down 
to  24  cubic  feet  per  H.P.  per  hour. 

1878.  SIMON  of  Nottingham  introduces  Brayton  cycle  in  England. 
Crossley  and  others  begin  extensive  manufacture  of  gas- 
engines  in  England. 

1885.  ATKINSON  Differential  Engine  appears  with  the  strokes  of 

the  cycle  of  differing  lengths. 

1886.  ATKINSON  Cycle  Engine  for  same  purpose  but  with  simpli- 

fied mechanism. 

1886.  PRIESTMAN  introduces  oil-engine. 
1892.  RUDOLPH  DIESEL  proposes  his  Rational  Motor. 
1892.   HORNSBY-AKROYD  oil-engine  appears. 
1895.  GOTTLIEB  DAIMLER  introduces  high-speed  motor. 

During  this  period  come  the  process  of  carburation  to 
utilize  liquid  fuels;  the  utilization  of  producer-gas  for 
power  purposes  and  the  development  of  power  from 
blast-furnace  and  coke-oven  waste  gases;  the  manu- 


1895 


facture  of  large-size  units  over  600  H.P.  by  John  Cockerili 


Co.  in  Belgium  and  by  Crossley  and  the  Premier  Engine 
in  England;  the  design  of  the  Westinghouse  throttling 
governor,  and  the  Sargent  engine  with  cut-off  governing, 
the  rise  of  the  natural  gas-engine  in  large  units,  and  the 
double-acting  gas-engine  with  compression  in  America. 


BIBLIOGRAPHY. 

250.  Note. — This  list  does  not  include  some  important 
sources  of  information  in  the  transactions  of  engineering  societies 
and  in  technical  journals,  notably  such  as  the  Zeitschrijt  des 
Vereins  Deutscher  Ingenieure,  London  Engineering,  and  the 
special  gas-engineering  and  automobile  periodicals.  For  these 
references  the  reader  is  referred  to  the  standard  technical  indices 
of  the  day.  It  covers  only  such  reference  literature  as  has  ap- 
peared in  book  form. 

STRUVE,  Paris,  1865.     La  Machine  a  Gaz. 

JOHN  BOURNE,  London,  1878.     Steam-,  Air-,  and  Gas-engines. 

MALLARD   et   LE    CH ATELIER,    Paris,    1883.       Recherches    experi- 

mentales  et  theoriques  sur  la  combustion  des  melanges  gazeux 

explbsifs. 

WM.  MACGREGOR,  London,  1885.     Gas-engines. 
THOS.  M.  GOODEVE,  London,  1887.     The  Gas-engine. 
KOHLER,  Leipzig,  1887.     Theorie  der  Gas-Motoren. 
WM.  ROBINSON,  London,  1890.     Gas-  and  Petroleum-engines. 
R.  SCHOTTLER,  Braunschweig,  1890.     Die  Gas-Maschine. 

(This  has  a  very  full  German  bibliography.) 
WEHRLIN,  Paris,  1890.     Moteurs  a  gaz  et  a  petrole. 
GUSTAVE   CHAUVEAU,   Paris,    1891.     Traite  theorique  et  pratique 

des  moteurs  a  gaz. 

GUSTAVE  RICHARD,  Paris,  1892, 1893, 1894.  Moteurs  a  gaz  et  a  petrole. 
RUDOLPH  DIESEL,  Berlin,  1893.     Theorie  und  Konstruction  eines 

rationellen  Warmemotors. 

PAUL  VERMAND,  Paris,  1895.     Les  moteurs  a  gaz  et  a  petrole. 

545 


54^  THE  GAS-ENGINE. 

AIME  WITZ,  Paris,  1895.     Traite  theorique  et  pratique  des  moteurs 

a  gaz  et  a  petrole.     2  vols. 
WM.    T.    BRANNT,    Philadelphia,    1896.     Petroleum    and    Natural 

Gas. 
RHYS    JENKINS,    London,    1896.     Index   to    Literature    on    Power 

Locomotion  on  the  Highway. 

BOVERTON  REDWOOD,  London,  1896.     Petroleum  and  its  Products. 
G.  LEICKFELD,  London,   1896.     Practical  Handbook  on  Care  and 

Management  of  Gas-engines.     Trans,  by  Geo.   Richmond. 
WM.    NORRIS,    London,     1896.     Practical    Treatise    on    the    Otto 

Cycle  Gas-engine. 

BRYAN  DONKIN,  London,  1896.     Gas-,  Oil-,  and  Air-engines. 
DUGALD  CLERK,  London,  1896.     The  Gas-  and  Oil-engine. 

(This  has  a  full  list  of  English  patents.) 
W.   C.   POPPLEWELL,   Manchester,    1897.     Elementary  Treatise  on 

Heat  and  Heat-engines. 

B.  P.  WARWICK,  Lynn,   1897.     The  Gas-engine. 
A.  J.  WALLIS-TAYLOR,  London,  1897.     Motor  Cars. 

ELLIOT  GRAFFIGNY,  New  York,  1898.     Gas-  and  Petroleum-engines. 

Louis  LOCKERT,  New  York,  1898.     Petroleum-motor  Cars. 

INTERNATIONAL  TEXT-BOOK  Co.,  Scranton,  1899.  A  Text-book 
on  the  Gas-engine. 

J.  F.  ALLEN,  Washington,   1900.     Automobile  Patent  Digest. 

E.  J.  STODDARD,   1900.     Gas-engine  Design. 

GOLDINGHAM,  New  York,  1900.  Design  and  Construction  of 
Oil-engines. 

W.  W.  BEAUMONT,  Philadelphia,  1900.  Motors  and  Motor  Vehi- 
cles. 

GARDNER  D.  Hiscox,  New  York,  1900.  Horseless  Vehicles, 
Automobiles,  and  Motor  Cycles. 

C.  C.    BRAMWELL,    New   York,    1901.     Construction    of    Gasoline 

Motor  Vehicles. 

GARDNER  D.  Hiscox,  New  York,  1901.     Gas-,  Gasoline-,  and  Oil- 
vapor-engines. 
(Full  list  of  American  patents.) 

E.  W.  ROBERTS,  Cincinnati,  1901.     The  Gas-engine  Handbook. 

E.  W.  LONGANECKER,  Indiana,  1902.     The  Practical  Gas  Engineer. 

ALFRED -C.  HARMSWORTH,  London,  1902.  Motors  and  Motor 
Driving. 

JAMES  E.  HOMANS,  New  York,  1902.     Self-propelled  Vehicles. 


BIBLIOGRAPHY.  547 

RUD  E.  MATHOT,  1905.  Modern  Gas-Engines  and  Producer  Gas 
Plants. 

C.  E.  LUCRE,  1905.     Gas-Engine  Design. 

RANKINE  KENNEDY,  1905.  Modern  Engines  and  Power  Genera- 
tors. 

A.  RIEDLER,  1905.     Gross  Gasmaschinen. 

H.  GALDNER,  1905.  Entwerfen  und  Berechnumg  der  Verbren- 
mungsmotoren . 

H.  HJEDER,  1904.     Die  Gas  Motoren. 

S.  S.  WYER,  1906.     Producer  Gas  and  Gas  Producers. 

E.  SOREL,  1904.  Carburation  et  Combustion  dans  les  Moteurs 
a  alcool. 

L.  PERISSE,  1905.     Les  Carburateurs. 

].  G.  M'INTOSH,  1907.     Industrial  Alcohol. 

J.  D.  ROOTS,  1899.     The  Cycles  of  Gas-  and  Oil-Engines. 

C.  E.  LUCRE,  1902.     The  Heat  Engine  Problem. 

S.  A.  Moss,  1906.     Elements  of  Gas-Engine  Design. 

L.  MARCHIS,  1905.     Moteurs  a  Essence  pour  Automobiles. 

D.  SIDERSRY,  1903.     Les  Usages  Industriels  de  I'alcool. 
PROFESSIONAL  PAPER  No.  48,  1906.     Report  on  Coal  Testing  Plant 

of  U.  S.  Geological  Survey  at  St.  Louis. 
GAS  POWER,  1903  to  date.     Pub.  at  St.  Joseph,  Mich. 


APPENDIX. 


LOGARITHMS. 

260.  In  arithmetical  computations,  the  usual  base  of  the  system  is  10, 
BO  that  x,  the  logarithm  for  a  number  tn,  will  be  the  exponent  to  which  10  is 
to  be  raised  to  give  the  quantity  tn,  or  x  =  logio  m.  In  analytical  mathe- 
matical work,  the  base  generally  employed  is  not  10,  but  is  represented  by 
f  whose  value  is  2.71828  +•  To  convert  common  or  Briggs  logarithms 
into  Napierian  logarithms,  the  former  are  to  be  multiplied  by  2.3026. 

The  equation  of  the  hyperbola  in  the  form  xy  =  constant  leads  to  the 
deduction  that  the  area  between  the  hyperbolic  curve  and  its  nearest 
asymptote  cut  off  by  two  ordinates  parallel  to  the  other  asymptote  and 
distant  respectively  from  the  origin  by  a  and  b  will  be  proportional  to 

log  — .      Hence  it  will  be  true  that  the  integral  of  —  will  be  the  hyperbolic 

Cl  X 

logarithm  of  x.     To  save  trouble  of  conversion,  a  table  is  appended  cover- 
ing the  usual  ranges  required. 


HYPERBOLIC    LOGARITHMS. 


No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

.01 

.0099 

.20 

.1823 

•39 

•  3293 

•58 

•4574 

•77 

•5710 

.02 

.0198 

.•21 

.1906 

.40 

•  3365 

•59 

•4637 

.78 

.5766 

.03 

.0296 

.22 

.1988 

•41 

•3436 

.60 

.4700 

•79 

.5822 

•04 

.0392 

•23 

.2070 

.42 

•  3507 

.61 

.4762 

.80 

•5878 

•05 

.0488 

•24 

.2151 

•43 

•3577 

.62 

•  4824 

.81 

•5933 

.06 

.0583 

•25 

•  2231 

•44 

.3646 

•63 

.4886 

.82 

.5988 

.07 

.0677 

.26 

.2311 

•45 

•37'6 

.64 

•4947 

•83 

.6043 

.08 

.0770 

•27 

.2390 

.46 

•3784 

.5008 

.84 

.6098 

.09 

.0862 

.28 

.2469 

•47 

•3853 

.66 

-5068 

•85 

.6152 

.10 

.11 

•0953 
.1044 

.29 

•3° 

.2546 
.2624 

.48 

•49 

.3920 
.3988 

.67 
.68 

.5128 
.5188 

.86 
.87 

.6206 

.6259 

.12 

•"33 

.1222 

•3i 
•32 

,2700 

.2776 

•50 
•51 

•4055 
.4121 

.69 
.70 

•5247 
.5306 

.88 
.89 

•6313 
.6366 

•  4 

.I3IO 

•33 

.2852 

•5* 

.4187 

.5365 

.90 

.6419 

•  5 

.1398 

•34 

.2927 

•53 

•4253 

.72 

•5423 

•  91 

.6471 

.  6 

.1484 

•35 

.3001 

•54 

.4318 

•73 

•92 

•6523 

:l 

.I|70 
•1655 

•36 
•37 

•3075 
.3148 

3 

•4383 
•4447 

•74 
•75 

•5539 
.5596 

•93 
•94 

•  6575 
.6627 

.19 

.1740 

•38 

.3221 

•57 

.76 

.5653 

•95 

.6678 

549 


APPENDIX. 


HYPERBOLIC    LOGARITHMS. 


No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

1.96 

.6729 

.66 

•  9783 

3-36 

.2119 

4.06 

.4012 

4-76 

.5602 

1.97 
1.98 

.6780 
•  6831 

.67 
.68 

.9821 
•  9858 

.2149 
.2179 

4.07 
408 

.4036 
.4061 

4-77 
4.78 

•5623 

1.99 

.6881 

.69 

•9895 

3-39 

.2208 

4.09 

•  4085 

4-79 

'5665 

2.OO 

.6931 

.70 

•9.933 

3-40 

.2238 

4.10 

.4110 

4.80 

.5686 

2.01 

.6981 

•71 

•99*59 

3  4i 

.2267 

4.11 

•4'34 

4.81 

•57°7 

2.  02 

.7031 

•72 

.0006 

3-42 

.2296 

4.12 

•4159 

4.82 

•5728 

2-03 

.7080 

•73 

.0043 

3-43 

.2326 

4-^3 

.4183 

4.83 

•5748 

2.04 

.7129 

•74 

.0080 

3-44 

•  2355 

4.14 

.4207 

4.84 

•5769 

2.05 

.7178 

•  -75 

.0116 

3-45 

.2384 

4-J5 

•4231 

4-85 

•5790 

2.o6 

.7227 

•76 

.0152 

•2413 

4.16 

.4255 

4.86 

•  5810 

2.07 

•7275 

•77 

.0188 

3-47 

.2442 

4  -i7 

•4279 

4-87 

•5831 

2.08 

•7324 

.78 

.0225 

3.43 

.2470 

4.18 

•43°3 

4.88 

•5851 

2.09 

•7372 

•79 

.0260 

3-49 

•2499 

4.19 

.4327 

4.89 

.5872 

2.10 

•74'9 

.80 

.0296 

3-50 

.2528 

4.20 

.4351 

4.90 

•  5892 

2.  II 

•7467 

.81 

•0332 

3-Si 

•2556 

4-21 

-4375 

4.91 

.5913 

2.12 

•7514 

.82 

.0367 

3-52 

•2585 

4.22 

.4398 

4.92 

•5933 

2.13 

•83 

.0403 

3-53 

.2613 

4.23 

.4422 

4-93 

•5953 

2.14 

!76o8 

.84 

.0438 

3-54 

.2641 

4.24 

.4446 

4-94 

•5974 

2.15 

•7655 

.85 

•  0473 

3-55 

.2669 

4.25 

.4469 

4-95 

•5994 

2.l6 

.7701 

.86 

.0508 

3  56 

.2698 

4.26 

-4493 

4.96 

.6014 

2.17 

•7747 

.87 

•°543 

3-57 

.2726 

4.27 

.45.6 

4-97 

.6034 

2.18 

•7793 

.88 

.0578 

3.58 

•2754 

4.28 

•454° 

4.98 

•  6054 

2.19 

•7839 

.89 

.06,3 

3-59 

.2782 

4.29 

•4563 

4.99 

.6074 

2.  2O 

.7885 

.90 

.0647 

3-60 

.2809 

4.30 

.4586 

5-00 

.6094 

2.21 

•793° 

.91 

.0682 

.2837 

4-31 

.4609 

5-or 

.6114 

2.22 

•"975 

92 

.0716 

3^2 

.2865 

4-32 

•4633 

5-02 

.6134 

2.23 

.8020 

•93 

.0750 

3-63 

.2892 

4-33 

.4656 

5.03 

.6154 

2.24 

.8065 

•94 

.0784 

3-64 

.  2920 

4-34 

.4679 

5-04 

.6174 

1:2 

.8109 
.8154 

•95 
.96 

.0813 
.0852 

|;§ 

•2947 
•  2975 

4,P 

.4702 
•4725 

5.05 

5-03 

.6194 
.6214 

2.27 

.8,98 

•97 

.0886 

3'67 

.3002 

4-37 

.4748 

5-07 

•6233 

2.28 

.8242 

.98 

.0919 

3-68 

.3029 

4-38 

.4770 

5.08 

.6253 

2.29 

.8286 

•99 

•  0953 

3.69 

.3056 

4-39 

•4793 

5-09 

.6273 

2.30 

•8329 

3.00 

.0986 

3.70 

.3083 

4.40 

.4816 

.6292 

2.31 

.8372 

.1019 

3.  7  1 

.3110 

4.41 

•  4839 

5-  :I 

.6312 

2.32 

.84.6 

3-03 

•  1O53 

3.72 

•3I37 

4.42 

.4861 

5-12 

.6332 

2.33 

•  8458 

3.03 

.1086 

3-73 

•3164 

4-43 

.4884 

5-'3 

•6351 

2.34 

.8502 

3-°4 

.  1119 

3-74 

•3*9* 

4  44 

.4907 

5-'4 

•6371 

.8544 

3.05 

.1151 

.3218 

4  45 

•  4929 

.6390 

2.36 

.8587 

3.06 

.1184 

3.76 

•3244 

4.46 

•4951 

5  J6 

.6409 

2.37 

.  862Q 

3-07 

.1217 

3-77 

.  327t 

4-47 

•4974 

5-l7 

.6429 

2.38 

^8671 

3.08 

.1249 

3.78 

•3297 

4.48 

.4996 

5-i8 

.6448 

2.39 

•8713 

3-°9 

.1281 

3-79 

•3324 

4-49 

.5059 

5-19 

.6467 

2.40 

•8755 

3.10 

•  1314 

3-8o 

•3350 

4-50 

.5041 

5-20 

.6487 

3.41 

.8796 

.1346 

•3376 

4-51 

.5063 

5-21 

.6506 

3.42 

.8838 

3.12 

.1378 

3^82 

•3403 

4-52 

•5085 

5-22 

•6525 

2.43 

.8879 

3.i3 

.1410 

3.83 

•3429 

4-53 

•5107 

5-23 

.6514 

••44 

.8920 

3-H 

.1442 

3.84 

•3455 

4  54 

•5129 

5.24 

.6563 

2.45 
2.46 

.8961 
.9002 

3-iS 
3-16 

.'474 
.1506 

3.85 
3.86 

•3507 

4-55 

•  5151 

5.25 
5.26 

.6582 
.6601 

2.47 

.9042 

•  X537 

3-87 

•3533 

4.57 

•5195 

5.27 

.6620 

2.48 

.9083 

3-  J8 

.1569 

3-88 

•  3558 

4.58 

•5217 

5.28 

.6639 

2.49 

.9123 

3-  X9 

.1600 

3-89 

.3584 

4-59 

•5239 

5-29 

.6658 

2.50 

.9163 

3-20 

.1632 

3-9° 

.3610 

4.60 

.5261 

5-30 

.6677 

2.51 

.9203 

3-21 

.1663 

3-91 

•3635 

4.61 

.5282 

5-31 

.6696 

2.52 

•9243 

3.22 

.1694 

3.92 

.3661 

4.62 

•5304 

5-32 

.6715 

2-53 

.9282 

3-23 

.1725 

3-93 

.3686 

4  63 

•5326 

5-33 

6734 

2.54 

.9322 

3-24 

.1756 

3-94 

•3712 

4.64 

•5347 

5-34 

.6752 

|| 

.9361 
.9400 

1:11 

.1787 
.1817 

3-95 
3.96 

•3737 
.3762 

4-65 
4.66 

•5369 
.5390 

5-35 
5.36 

.6771 
.6790 

•9439 

3-27 

.1848 

3-97 

.3788 

4.67 

.5412 

5-37 

.6808 

2.58 

•9478 

3-28 

.1878 

3-98 

•3813 

4.68 

•5433 

5.38 

.6827 

2.59 

•95*7 

3-2^ 

.1909 

3-99 

.3838 

4.69 

•5454 

5-39 

.6845 

2.60 

•9555 

•'939 

4.00 

•3863 

4.70 

•  5476 

5-4° 

.6864 

2.61 

•9594 

3'S1 

.1969 

4.01 

.3888 

4-71 

•5497 

5-41 

.6882 

2.62 

.9632 

3-32 

.1999 

4.02 

.3913 

4.72 

.5518 

5-42 

.6901 

2.63 

.9670 

3-33 

.2030 

4.03 

.3938 

4-73 

•5539 

5-43 

.6919 

2.64 

.9708 

3-34 

2060 

4.04 

.3962 

4-74 

5-44 

.6938 

».65 

.9746 

3-35 

.2090 

4-  o.S 

•3987 

4-75 

•558i 

5-4S 

.6956 

APPENDIX. 


551 


HYPERBOLIC    LOGARITHMS. 


No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

5-46 

•6974 

6.16 

.8181 

6  86 

•9257 

7-56 

.0229 

8.32 

.1187 

5-47 

•6993 

6.17 

.8197 

6.87 

.9272 

7-57 

.0242 

8-34 

.1211 

5.48 

.7011 

6.18 

.82.3 

6.88 

.9286 

7-58 

•0255 

8-36 

•!235 

5-49 

.7029 

6.  ,9 

.8229 

6.89 

.9301 

7-59 

.0268 

8.38 

.1258 

5-5° 

.7047 

6.20 

•  8245 

6.90 

•93'5 

i  7-6o 

.0281 

8.40 

.  1282 

5-5* 

.7066 

6.21 

8262 

6.91 

•9330 

7.61 

.0295 

8  42 

.1306 

5.52 

.7084 

6.22 

.8278 

6.92 

•9344 

7.62 

.  0308 

8.44 

.1330 

5-53 

.7102 

6.23 

.8294 

6-93 

•9359 

7.63 

.0321 

8.46 

•*353 

5.54 

.7120 

6.24 

.8310 

6.94 

•9373 

7.64 

•0334 

8.48 

•X377 

I'll 

•  7138 
•7I56 

6.25 

6.20 

.8326 
•  8342 

6-95 
6.96 

•9387 
.9402 

7-65 
7.66 

•0347 
.0360 

8.50 
8.52 

.1401 
.1424 

5-57 

•7*74 

6.27 

•8358 

6-97 

.9416 

7-67 

•0373 

8-54 

.1448 

J5-58 

.7192 

6.28 

•8374 

6.98 

.9430 

7.68 

.0386 

8.56 

.1471 

5-59 

.7210 

6.29 

.8390 

6-99 

•9445 

7.69 

•0399 

8.58 

•H94 

5-6o 

.7228 

6.30 

.8405 

7.00 

•9459 

7.70 

.0412 

8.60 

.1518 

J.6i 

.7246 

6.31 

.8421 

7.01 

•9473 

7.71 

.0425 

8.62 

•J54i 

5-62 

.7263 

6-32 

.8437 

7.02 

.9488 

7.72 

•  0438 

8.64 

.1564 

5-63 

.7281 

6.33 

•8453 

7-°3 

.9502 

7-73 

.0451 

8.66 

•1587 

5-64  ' 

•7299 

6-34 

.8469 

7.04 

.9516 

7-74 

.0464 

8.68 

.1610 

§ 

•73»7 

•7334 

6.3"! 
6.36 

.8485 
.8500 

7-05 
7.06 

•9530 
•9544 

7-75 
7.76 

.0477 
.0490 

8.70 
8.72 

•xj>33 
.1656 

5-67 

•7352 

6.37 

.8516 

7.07 

•9559 

7-77 

•0503 

8.74 

.1679 

5-68 

•737° 

6.38 

.8532 

7.08 

•9573 

7.78 

.0516 

8.76 

.1702 

5-69 
5-7° 

•7387 
74°5 

6.39 
6.40 

.8547 
•8563 

7.09 

7.10 

•9587 
.9601 

7-79 
7.80 

.0528 
.0541 

8.78 
8.80 

•1725 
.1748 

5  71 

.7422 

6.41 

•8579 

7.11 

.9615 

7.81 

•0554 

8.82 

.1770 

5-72 

.7440 

6.42 

•8594 

7.12 

.9629 

7.82 

.0567 

8  84 

•1793 

5-73 

•  7457 

6.43 

.8610 

7-i3 

•9643 

7-83 

.0580 

8.86 

.1815 

5-74 

•7475 

6-44 

.8625 

7.14 

•9657 

7.84 

.0592 

8.88 

.1838 

5-75 

.7492 

6-45 

.8641 

7-I5 

.9671 

7-85 

.0605 

8.90 

.i86r 

5-76 

•  7509 

6.46 

.8656 

7.16 

.9685 

7.86 

.0618 

8.92 

.1883 

5-77 

•7527 

6.47 

.8672 

7.17 

.9699 

7.87 

.0631 

8.94 

.1905 

5.78 

•7544 

6.48 

.8687 

7-18 

•9713 

7.88 

.0643 

8.96 

.1928 

5-79 

•756i 

6.49 

.8703 

7.19 

.9727 

7.89 

.0656 

8.98 

.1950 

5-80 

•7579 

6.50 

.8718 

7.20 

•9741 

7.90 

.0669 

9.00 

.1972 

5-8i 

.7596 

6.51 

.8733 

7.21 

•9754 

7.91 

.0681 

9.02 

.1994 

5-82 

•7613 

6.52 

.8749 

7.22 

.9769 

7.92 

.0694 

9.04 

.2017 

5.83 

.7630 

6.53 

.8764 

7-23 

.9782 

7-93 

.0707 

9.06 

•2039 

5.84 

.7647 

6-54 

.8779 

7.24 

.9796 

7-94 

.0719 

9.08 

.2061 

5.85 

.7664 

6-55 

.8795 

7-25 

.9810 

7-95 

.0732 

9.10 

•2083 

5-86 

.7681 

6.56 

.8810 

7  26 

.9824 

7.96 

.0744 

9.12 

.2105 

5.87 

.7699 

6.57 

.8825 

7.27 

.9838 

7-97 

•°757 

9.14 

.2127 

5-88 

.7716 

6.58 

.8840 

7.28 

.9851 

7-98 

.0769 

9.16 

.2148 

5.89 

•7733 

6-59 

.8856 

7.29 

.9865 

7'99 

.0782 

9.18 

.2170 

5-9° 

•775° 

6.60 

.8871 

7-3o 

•9879 

8.00 

.0794 

9.20 

.2192 

5-9i 

.7766 

6.61 

.8886 

7-3i 

.9892 

8.01 

.0807 

9.22 

.2214 

5-92 

-7783 

6.6a 

.8901 

7-32 

.9906 

8.02 

.0819 

9.24 

•2235 

5-93 

.7800 

6.63 

.8916 

7-33 

.9920 

8.03 

.0832 

9.26 

•2257 

5-94 

•  7817 

6.64 

-893^ 

7-34 

•9933 

8.04 

.0844 

9.28 

.2279 

5-95 
5.96 

•7834 
•  7851 

6.65 
6.66 

.8946 
.896! 

7-35 
7-36 

•9947 
.9961 

8.05 
8.06 

0857 
.0869 

9-3° 
9-32 

.2300 
.2322 

5-97 

.7867 

6.67 

.8976 

7-37 

•9974 

8.07 

.0882 

9-34 

•2343 

5.98 
5'99 

.7884 
.7901 

6.68 
6.69 

.8991 
.9006 

7-38 
7-39 

.9988 
.0001 

8.08 
8.09 

.0894 
.0906 

9-36 
9-38 

.2364 
•2386 

6.00 

.7918 

6.70  - 

.9021 

7.40 

.0015 

8.10 

.0919 

9.40 

.2407 

6.01 

•7934 

6.7* 

.9036 

7.41 

.0028 

8.  ii 

.0931 

9.42 

.2428 

6.02 

•7951 

6.72 

.9051 

7.42 

.0041 

8.12 

•0943 

9-44 

.2450 

6.03 

.7967 

6-73 

.9066 

7-43 

•°°55 

8-13 

.0956 

9.46 

.2471 

6.04 

.7984 

6-74 

.9081 

7-44 

.0069 

8.14 

.0968 

9-48 

.2492 

6.05 

.8001 

6.  75 

•9095 

7-45 

.0082 

8.15 

.0980 

9-5° 

•2513 

6.06 

.8017 

6.76 

.9110 

7.46 

.0096 

8.16 

.0992 

9-52 

2534 

6.07 

.8034 

6-77 

.9125 

7-47 

.0108 

8.17 

.1005 

9'54 

•2555 

6.08 

.8050 

6.78 

.9140 

7.48 

.0122 

8.18 

.1017 

9-56 

.2576 

6.09 
6.10 

.8066 
.8083 

6-79 
6.80 

•  9155 
.9169 

7-49 
7-5° 

•0136 
.0149 

8.19 

8.20 

.1029 
.  1041 

9.58 
9  60 

•2597 
.2618 

6.  ii 

.8099 

6.81 

.9184 

7-51 

.0162 

8.22 

.1066 

9.62 

.2638 

6.12 

.8116 

6.82 

.9199 

7-52 

.0176 

8.24 

.1090 

9  64 

•2659 

tf.i3 

.8132 

6.83 

.9213 

7-53 

.0189 

8.26 

.1114 

9.66 

.2680 

6.14 

.8148 

6.84 

.9228 

7-54 

.O2O2 

8.28 

.1138 

9.68 

.2701 

6.15 

.8165 

6.85 

.9242 

7-55 

.02Ti; 

8.30 

.1163 

9.70 

.2721 

552 


APPENDIX. 


HYPERBOLIC    LOGARITHMS. 


No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

No. 

Log. 

9.72 

.2742 

10.25 

•3*79 

14.00 

.6391 

21 

3-0445 

3~ 

3-5835 

9-74 

.2762 

10.50 

•35'3 

14-25 

.6567 

22 

3.0910 

37 

3.6109 

9.76 

•2783 

10.75 

•3749 

14-5° 

.6740 

23 

3-  '355 

33 

3-6376 

9.78 

.2803 

11.00 

•3979 

14-75 

.6913 

24 

3.1781 

39 

3-6636 

9.80 

.2824 

11.25 

.4201 

15.00 

.7081 

25 

3-2189 

40 

3.6889 

9.82 

.2844 

11.50 

-4430 

15-50 

.7408 

26 

3.2581 

4i 

3-7*l6 

9.84 

.2865 

11-75 

-4636 

16.00 

.7726 

27 

3-2958 

42 

3-7377 

9.86 

.2885 

12.00 

•4849 

16.50 

.8034 

28 

3-3322 

43 

3  7612 

9.88 

.2905 

13.25 

•5052 

17.00 

.8332 

29 

3-3673 

44 

3-7842 

9.90 

.2925 

12.50 

.5262 

17-50 

.8621 

30 

3.4012 

45 

3-8067 

9.92 

.2946 

12-75 

•5455 

18.00 

.8904 

31 

3-434° 

46 

3.8286 

9-94 
9.96 

.2966 
.2986 

13.00 
13-25 

•5649 
.5840 

18.50 
19.00 

•9i73 
•9444 

32 
33 

3-4657 
3-4965 

47 
48 

3-8501 
3-8712 

9.98 

.3006 

I3-50 

.6027 

19.50 

2.9703 

34 

3-5263 

49 

3-8918 

10.00 

.3026 

13-75 

.6211 

20.00 

2-9957 

35 

3-5553 

So 

3-9i» 

INDEX. 


Absolute   Temperature   117 

Acetylene  explosion  experiments 518 

Acetylene  gas  64 

Adiabatic  expansion 131 

Adjustable  valves  for  proportioning  mixtures 213 

Advancing   spark   arrangement 259 

Advantages  of  internal  combustion 163 

Air,  analysis   of   22 

Air   as   medium   in  heat-engine 6 

Air-cooled   automobile   motor 201 

Air-cooled  bicycle   motor 199 

Air    for    combustion 22 

Alcohol   carburetors   245 

Alcohol   engine  207 

Alcohols    90 

Analysis  of  a  power-plant 9 

Analysis    of    cycles 346 

Analysis   of   gas 101 

Analyzed  fuel,  combustion  of 26 

Arc  ignition 260 

Atkinson   differential   engine 345 

Atkinson  cycle   engine 375 

Automobile  engines 198 

Automobile  carbureters 236 

Automatic  carburetors 236 

Automatic  mixing  by  suction 212 

Available   energy   119 

Axiom  carbureter  233 

Beau  de  Rochas  cycle 158,  379 

Berthelot  and  Vielle  experiments  on  explosive  waves 526 

Bibliography  of  the  gas-engine , 545 

553 


554  INDEX. 


Bicycle   motor   199 

Blast-furnace  gas 65 

Boiling-point  of   hydrocarbons 88 

Bomb  calorimeter " i 33 

Boyle's  law 116 

Brake  horse-power 124,  318 

Bray  ton   carburetor 226 

Brayton  cycle 163,  389 

Brayton  engine 497 

Brouhot  alcohol   carbureter : 245 

Calculated   temperature   of   combustion 119,  143,  472 

Calorie,  value  of 105 

Calorific  power 30 

Calorimeters 33 

Carbon,  combustion  of 22 

Carburation 221 

Carburation,    unsatisfactory 310 

Carbureters    221 

Carnot   ideal   cycle 154,  412 

Carnot  usual  cycle 401 

Catalytic  ignition : 252 

Cayley's  principle  of  heating 8 

Clearance  volume.. 286,  481 

Clerk  engine 174 

Clerk  explosion  experiments 504 

Climate,  effects  of,  on  mixture 219 

Coal-gas  64 

Coke-oven  gas 71 

Cold  carbureters 311 

Collapsible  chamber   for   gas-engines 212 

Combustion    10 

Combustion  chamber,  volume  of 286,  481 

Combustion  of    analyzed    fuel 26 

Combustion  of   explosive  mixtures 486 

Combustion   ratio 26 

Comparison  of  types  of   engine 184 

Compound  gas-engine 187 

Compound   gas-engine,   cycle 375 

Compounds,   combustion   of 23 

Compressed  air   for  restarting 305 

Compression  ignition 255 

Compression  pressure,  usual 286,  479 


INDEX.  555 


Computed  temperature  of  combustion 41,  119,  472,  336 

Conclusions  from  analysis  of  cycles 463 

Constant-level    carburetor 232 

Constant-pressure  heating-engines 485 

Constant-pressure  specific  heat 139 

Constant-volume  specific  heat 139 

Contact  system  of  ignition 260 

Continuous  rotative  motor 151 

Control  of  carburetor  for  proportioning 216 

Converted  gas-engine 205 

Cooling  of  cylinder 279 

Corrosion  due  to  alcohol 97,  313 

Cost  of  operation 529 

Cracking  of   hydrocarbons 88 

Crank-pin  effort  in  Otto  cycle 161 

Cut-off  governing 273 

Cycle  defined -  152 

Cycle  of  Brayton — -  162 

Cycle  of  Carnot 154 

Cycle  of  Diesel 163 

Cycle  of  internal-combustion  engine 157 

Cycle  of  Otto   I 158 

Cycle  of  steam-engine   153 

Cycle  with  arbitrary  heating 416 

Cycle  with  atmospheric  heating 417 

Cycle  with  isometric  heating 375 

Cycle  with  isopiestic  heating 389 

Cycle  with  isothermal  heating  411 

Cycles   classified  158 

Cyclic  analysis  351 

Cylinder  volumes,  design  of _— _ 110,  480 

Daimler  automobile  motor 201 

Daimler  carbureter  229 

De  Dion  carburetor  223 

Deductions  from  pressure  analysis 445 

Deductions  from  temperature  analysis 434 

Deductions  from  volume  analysis 452 

De  Mondesir  experiments  on  explosive  waves 526 

Denatured  alcohol 92,  96,  207 

Design  of  cylinder  volumes  110,  480 

Depreciation  of  plant 532 

Diagram  factor 476 


556  INDEX. 

PAGE 

Diesel  cycle  163,  401 

Diesel   engine  193 

Diluent  gas,  effect  of 19,  509 

Dilution  of  gas-mixture 98 

Disadvantages  of  internal  combustion 167 

Dissociation  43 

Double  opposed  motors 185 

Dowson  producer-gas 52 

Dynamo-electric  ignition 262 

Economy  records 341 

Effective  pressure,  theoretical  mean 105,  333,  469 

Effecti.ve  specific  heat 141 

Efficiency  121 

Efficiencies  of  various  cycles 455 

Electric  ignition 256 

Elements  of  cost 531 

Elliot's  apparatus  for  gas  analysis 101 

Entropy  temperature  diagram 346 

Ethyl  alcohol 90 

Exhaust-gases  322,  292 

Exhaust  temperatures  322 

Expansive  working 128 

Explosion 15 

Explosion  waves  in  engine  diagram 332 

^Explosion  waves,  propagation  of 526 

Explosive  mixtures,  combustion  of 486 

Explosive  mixtures,  test  of 502 

Exponent  in  equation  for  expansion 147 

External    heating 7 

Expense,  elements  of 531 

Factors  affecting  mean  effective  pressure ,_  476 

Failures  of  engines 308 

Failures  of  ignitions 309 

Flame 11 

Flame-cap 17 

Flame-cap  in  cumbustion  486 

Flame  ignition 250 

Flannel  carburetors 225 

Float  carburetor 232 

Fuel  expense 534 

Fuel-oil   .  .    86 


INDEX.  557 

PAGE 

Gas,  acetylene 64 

Gas,  analysis* 102 

Gas,  analysis  and  properties  of _ 71 

Gas,  blast-furnace 65 

Gas-burning  engines 171 

Gas,  coke  oven 71 

Gaseous  fuel,  sources  of 43 

Gas,  illuminating  or  coal 64 

Gas,  natural 44 

Gasoline 88 

Gasoline  motors 198 

Gas,  Pintsch 86 

Gas,  producer 45 

Gas,  turbine 151,  500 

Gas,  water 50 

Gay-Lussac  law  115 

Gentey's  system  of  heating 8 

Gibbs  gas-engine  with  constant-pressure  heating 495 

Gobron-Brillie  alcohol-motor 208 

Governing 264 

Governing  in  Westinghouse  engine 179 

Graphical  results  of  cycle  analysis , 425 

Grashof's  formula  for  specific  heat 142 

Gravity,  force  of 1 

Grover's  acetylene  experiments 518 

Grover's  experiments  on  neutrals 522 

Grover's  M.  E.  P.  formula  109,  480 

Guarantee  of  performance 126,  540 

Hammer-break  ignition : 260 

Hirsch  engine 193 

Historical  summary 543 

Hit-or-miss  governor 266 

Hornsby-Akroyd  oil-engine 189 

Horse-power,  value  of  105 

Hot-tube  ignition 252 

Huzelstein  carburetor 234 

Hydrocarbons,  analysis  and  properties  of 26,    82 

Hydrocarbons,  constitution  of 25 

Hydrogen,  combustion  of 23 

Hyperbolic  logarithms  550 

Ignition 15,  250 

Ignition  failures _  309 


558  INDEX. 

PAGE 

Ignition  temperatures 523 

Illuminating-gas  _ 64 

Impoverishing  charge 267 

Incandescence   11 

Incomplete  combustion 12 

Indicator  diagram  of  Otto  cycle . , 158 

Indicator  for  gas-engine 320 

Inertia  of  valves,  effect  of 219 

Inflammation   temperatures    523 

Injection  of  water,  for  cooling 279 

Insurance  risk  with  internal-combustion  engines 165 

Insurance,  cost  of 534 

Internal-combustion  method 7 

Interest  on  cost  of  plant 532 

Intrinsic  energy  119 

Isobaric  lines  134 

Isometric  lines   134 

Isopiestic  lines . 134 

Isothermal  expansion 130 

James-Lunkenheimer  carburetor 233 

Japy  alcohol-carburetor 245 

Jump-spark  ignition  256 

Junker  calorimeter 35 

Kerosene 86 

Kerosene  carburetor 247 

Kerosene  engine 188 

Knox  automobile  motor 201 

Korting  engine 177 

Labor  expense 534 

Lanchester  starting  device 305 

Langan   free-piston  engine  cycle  354 

Launch-engine  using  gasoline 204 

Leakages  in  engines  313 

Leakages  of  hydrocarbons 89 

Lencauchez  producer-gas 54 

Lenoir  engine  cycle 353 

Liquid  fuel  84,     85 

Logarithms,  hyperbolic ___ ' 550 

Log-blank  for  gas-engine  test 327 

Longuemare  carburetor 231 


INDEX.  559 

PAGE 

Losses   in   gas-engines   344 

Lowe  gas 52 

Lozier  engine 180 

Lubrication  of  engines  307 

Lucke  apparatus  for  combustion  of  explosive  mixtures 486 

Lucke  apparatus  to  observe  volume  increase 499 

Lucke  calorimeter 39 

Lucke  explosion  experiments 507 

Lucke  formulae  for  mean  effective  pressure 471 

Lucke  kerosene-engine 195 

Magneto-electric  ignition 262 

Mahler  calorimeter 33 

Make-and-break  ignition 260 

Mallard  and  Le  Chatelier  explosion  experiments 523 

Maintenance  expense  533 

Manipulation  of  engines 297 

Marienfelde  alcohol  carburetor 245 

Mariotte  law 115 

Marsh  bicycle  motor  199 

Martha  carburetor 245 

Massachusetts  Institute  of  Technology,  explosion  experiments 514 

Maybach's  carburetor 230 

Mean  effective  pressure 105 

Mean  effective  pressure  in  cycles 105,  333,  440,  469 

Mean  effective  pressure  observed 333 

Mean  effective  pressure,  theoretical 470 

Mechanical  design  of  gas-engines 483 

Mechanical  efficiency 124 

Mechanical  equivalent  of  heat 104 

Mechanically  operated  valves 214 

Media  in  heat-engines  4 

Methyl  alcohol 90 

Mietz  and  Weiss  kerosene-engine 191 

Misfiring 314 

Mixtures  in  internal-combustion  engines 211 

Mond  producer-gas 49 

Morgan  blast-furnace  gas-engine 66 

Mosler  carburetor -. 236 

Mufflers 294 

Muscular  force 1 

Nash  engine 175 

Natural  gas  44 


560  INDEX. 


Neutral  gas,  effect  of 19 

Neutrals,  effect  of  508 

Oil,  expense  of 533 

Olds  carburetor 228 

Orsat's  apparatus  for  gas  analysis 102 

Otto  engine  cycle 158,  375 

Otto  silent  engine 171 

Overhead  charges  535 

Oxygen  for  combustion 21 

Performance  records 341 

Petroleum,  refining  of 85 

Phase  denned  '  152 

Phoenix  carburetor  231 

Pintsch  gas 86 

Piston  motor . 105 

Power-plant,  analysis  of 4 

Pre-ignition  in  governing 272 

Pressure  analysis  of  cycles 436 

Pressures  due  to  explosion 505 

Pressure,  theoretical  mean  effective 105,  333,  469 

Priestman  oil-engine 188 

Producer-gas  45 

Products  of  combustion 25,  97,  102 

Propagation  of  flame 15,  481,  525 

Proportioning  of  mixtures  of  air  and  fuel 211 

Proportions  of  fuel  and  air 100 

Pump-cylinders  for  proportioning 215 

PV  diagram  114 

Ratib  of  specific  heats 143 

Records   of   performance   341 

Reeve  burner 495 

Refining  of  petroleum  85 

Renewal  expense  533 

Repair  expense 533 

Restarting  of  engines 302 

Richard  alcohol-carburetor 245 

Scavenging  engines 186 

Scavenging  for  proportioning 216 

Schloesing  experiments  on  explosive  waves  526 


INDEX.  5i 

PAGE 

Schmid  and  Beckfeld  gas-engine 495 

Secor  kerosene-engine 190 

Shaw's  system  of  heating 8 

Silencers   294 

Sinking  fund 532 

Simpson's  rule  for  areas 115 

Smoke   14 

Sources  of  gaseous  fuel 43 

Sources  of  heat  energy 6 

Sources  of  motor  energy 1 

Sparking  plug  and  coil 251 

Specific  heat 136,  141 

Spontaneous  combustion ' 21 

Spray  carburetors  229 

Starting  of  engines 298 

Steam-engine  cycle 153 

Stopping  of  engines  301 

Storage  of  energy  in  gas  or  liquid  fuel 165 

Subdivided  power  with  gas-  or  oil-engines 165 

Supplies,  expense  of 534 

Surface  carburetor  223 

Tandem  double-acting  engine  180 

Taylor  gas-producer 49 

Temperature  analysis  of  cycles  429 

Temperature  change  in  adiabatic  expansion 133 

Temperature  entropy  diagram 346 

Temperature  of  combustion  41,  119,  336,  472 

Temperature  of  exhaust 322 

Temperature  of  ignition 523 

Testing  of  gas-engines 319 

Theoretical  mean  effective  pressure  105,  333,  469 

Thermal  efficiency 121 

Thermal  lines  134 

Thermal  unit,  value  of 105 

Theta-phi  diagram 346 

Throttling  as  means  of  governing 267 

Throttling  exhaust  in  governing 269 

Tide  motors,  limitations  of 2 

Total  energy 119 

Turbine  gas-engine  151,  500 

Twin  tap  on  carburetors 224 

Two-cycle  engine 180 

Types  of  engine  compared _  184 


562  INDEX. 

PAGE 

Universal  carburetor > 234 

Value  of  exponent  N 147,  332 

Value  of  R 136 

Vaporizer  in  carburetor 247 

Vapors  as  media 5 

Variations  in  cycle  ____157,  170,  351 

Variations  in  mixtures,  effect  of 217 

Variations  in  speed,  effect  of 218 

Velocity  of  flame  propagation 486 

Velocity  of  mixture  through  valves  483 

Ver  Planck  kerosene-engine 195 

Vibrator  for  igniting  coil 258 

Volume  analysis  of  cycles 446 

Volume  of  clearance 286,  481 

Volume  of  combustion-chamber 236,  481 

Volume  of  cylinder 110,  480 

Water-gas 50 

Water-cooled  motor 201 

Water  cooling 280 

Water,  cost  of  534 

Water  for  cooling , 233 

Water  motors,  limitations  of 2 

Westinghouse  engines 177 

Westinghouse  governor 179 

Wick  carburetors 225 

Wilcox  gas-engine  with  constant-pressure  heating 494 

Windmills,  limitations  of 2 

Winton  governor 268 

Work  done  in  various  cycles 455 


OF  THE 

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